HECU cosplay list:

A quick list of what I was wearing:
1. PASGT Helmet replica + helm-cover + cat-eyes band
2. S10 gas mask + NATO filter + green-tinted outserts (optional: S10 flash hood)
3. ALICE Pack (large size)
4. parts of a rig that the seller calls "US Navy Seal CQB LBV Modular Assault Vest"
5. Paintball "chest protector"
6. Urban camo overall
7. Police/security/military purpose boots (black)
8. Smartphone attached to ALICE shoulder strap.
9. Fingerless biker gloves (with holes for knuckles)
10. Military bag for helmet(/gasmask)
11. Drop leg pistol holster (+pockets) (Universal holster suitable for most pistol frames.) (black)
12. Black shotgunner/massn-style balaclava around my neck.
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Details:

1.
PASGT Helmet replica from aliexpress.com (got one with a visor. (the visor can easily be removed or re-attached with a screwdriver + adjustable wrench))I got a black one, because I'd prefer that color when I'm using it without a helmet cover (for other occasions like umbrella/SAS/police cosplays).
This replica is lightweight so it's very comfortable to wear. The helmet I got is better and more comfortable than the pictures show and I'm very happy with it! (it has much better comfort for the top of the head than pictured, and a different more comfortable chin-strap than what is shown on the pics.)(if your head is smaller than the average human head-size then the helmet is possibly too big for you.) I got my helmet from this seller here:    https://www.aliexpress.com/item/1005005748402046.html?gps-id=pcStoreJustForYou&scm=1007.23125.137358.0&scm_id=1007.23125.137358.0&scm-url=1007.23125.137358.0&pvid=873b82d7-0a9c-49c6-80a8-dfb4e6ddb849&_t=gps-id:pcStoreJustForYou,scm-url:1007.23125.137358.0,pvid:873b82d7-0a9c-49c6-80a8-dfb4e6ddb849,tpp_buckets:668%232846%238112%231997&pdp_npi=4%40dis%21SEK%21835.67%21409.45%21%21%2172.76%21%21%402101eeda16953747355108381e601d%2112000034206214901%21rec%21SE%212734282065%21&spm=a2g0o.store_pc_home.smartJustForYou_723259204.0

PASGT helmet cover (us woodland camo) https://www.tacticalgeartrade.com/us-army-m88-pasgt-helmet-cover-camo-woodland.html( I still want to get my hands on a PASGT helm-cover that is mostly just green with some black/dark, and/or urban/winter camo helm-cover)
cat-eyes band for helmet. https://www.tacticalgeartrade.com/us-army-helmet-reflective-cat-eyes-band-od-pasgt-mich.html

tacticalgeartrade.com say on their website that they are selling PASGT helmet replicas, but they did not ship the helmet to me. They did ship everything else i ordered from there though (and gave me a refund for the helmet they did not ship to me (after i asked about the missing helmet)). Items from them were mostly in good condition, but some item(s) might be in a condition where you can see it has been stored for a long time (or possibly used a little), or/and some minor flaw like som tiny part missing (e.g. one tiny zipper pull missing). The price for some of their items is very cheap though. It seemed like they shipped it as a gift. From china.
They sell a variety of bags (that you might want to use for a HECU cosplay) etc,some for a very cheap price: https://www.tacticalgeartrade.com/tactical-gear/bag-case/waist-bag.html
if you want the real (and more heavy and expensive) thing you can ofc buy a real PASGT helmet!

2.
S10 Gasmask (produced 2010 (the last S10 produced is from 2012 I think)) + NATO filter ( I strongly advice getting a sealed unused filter, only using filters no one other than you have used.)
You could get an S10 gas mask on Ebay, (used, not brand new). I'm using a size 2, which is the most common size. ( I cleaned the S10 like in this video right after I took the gas mask out of the package: https://www.youtube.com/watch?v=AWxchTehWMo )

The chinese FMJ08 gas mask would resemble the hgrunt gas mask even better,
and I've recently found a seller who provides green-tinted lense outserts for the FMJ08/MF20/MF22 (although expensive!)
https://www.etsy.com/de-en/listing/1505475432/eye-covers-s10-mf20-gas-mask-rubber-gear?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=s10+gas+mask&ref=sr_gallery-1-16&sts=1&organic_search_click=1&variation0=3786135076&variation1=3656623489

I currently only have green outserts for the S10 (they will not work for the FMJ08, I've tried), which i bought from here (as well as black+red+mirror ones for other occasions):    https://www.ebay.com/itm/295827376199?hash=item44e0af8847:g:5AYAAOSwOctkuOTK&amdata=enc%3AAQAIAAAAwE5PlxhgeWW%2F1rAYzpaQBOMdj1Tn4ItCdMLFQEh6w4Sdtuzw8pVTGzKtK%2BqoSwpR25Ps%2B8SH8oc1Q2ZyMggVqDEa6iapBYkcnuGBQq%2FDCqOR2n0k6s2fh3FmxEpzcHZpuxZqnUIVvkhltGqlMEQk5qrKZPVrJqjY0KHaxkwvC%2Fx5xq%2Bvni6vX%2BIkvRW5%2BKRcwPxcrIuN9oxGN%2FMTeEy8yNQhwbT7NWj9NJib5eajXaFxTgD97FVlAVuNa6B6oLVwuQ%3D%3D%7Ctkp%3ABk9SR4SJicrXYg

I have an FMJ08 gas mask, and they are possible to buy in unused condition, from aliexpress.com , as well as unused sealed chinese military filters for it. (they shipped what I ordered from them in good new condition.)
https://www.aliexpress.com/item/1005004443255134.html?gps-id=pcStoreJustForYou&scm=1007.23125.137358.0&scm_id=1007.23125.137358.0&scm-url=1007.23125.137358.0&pvid=39c0bffd-158a-4011-986d-6adf4e27d2f4&_t=gps-id:pcStoreJustForYou,scm-url:1007.23125.137358.0,pvid:39c0bffd-158a-4011-986d-6adf4e27d2f4,tpp_buckets:668%232846%238112%231997&pdp_npi=4%40dis%21SEK%21397.97%21198.93%21%21%2134.65%21%21%402101eeda16953748175711247e601d%2112000029197281241%21rec%21SE%212734282065%21&spm=a2g0o.store_pc_home.smartJustForYou_2002106532451.1

in one of the pics i posted I'm also wearing a flash hood for the S10, (the military "one-size-fits-all", but it's not an optimal fit/size for the gas mask it is intended for... but has a bit of real flame-resistance function at least).(You can get a new unused one on Ebay, but they are expensive!)There might be S10 flash hood replicas for sale that actually fits the gas mask better (but without the flame-resistance function).

3.
ALICE Pack, LC-2, large (with Shoulder Straps, Waist Belt and pack ram (all meant for the ALICE pack))
(you could go with a medium ALICE Pack too, (I'm not 100% sure how it would look,) but I like the look of HECU with large size packs,)

The large ALICE pack can be adjusted and tightened to make it take up less volume (while still looking neat) to match the ALICE pack sizes in the above pictures pretty well. And owning a large ALICE pack can be really useful at times.  ( I had not filled up the pack properly during the time the pics were taken. )

I have the shoulderstraps attached in an unusual way, (to the ALICE pack waist belt,) to give the HECU style look. I find this style of wearing the pack to be comfortable, but you then need to keep the waist belt on.

ALICE packs can be found on www.Ebay.com , typically in used condition. Make sure you get one in a condition you will be ok/happy with. They can get pretty expensive if you find one in a good condition, as the originals are no longer produced. There are replicas of them though in new condition. I went for an original ALICE pack, used but in good/ok condition (advertised as "mint" condition), large.

As the pics taken were unplanned and spontaneous I didn't fill up my ALICE pack as much as I should have. I think it will look better when I do.

4.
the waist-pouches is a cheap "in stock" option for now,
https://www.tacticalgeartrade.com/us-navy-seal-cqb-lbv-modular-assault-vest-od.html
I detached the upper parts and folded in the flaps above the pouches, and wore it around my waist. (The olive color is brighter than i want it to be, but it does have the same color as the ALICE pack shoulder straps.)
the "US Navy Seal CQB LBV Modular Assault Vest"
is pretty much what HUNK from Resident Evil is wearing.
(I also have a black version of this one for other cosplays like Black ops Massn/Umbrella soldier.)
(these seemed like a nice option for HECU:  https://www.tacticalgeartrade.com/us-army-delta-elite-seal-molle-hydration-vest-od.html  but they are out of stock atm and have been for at least some months now, so I don't know if they will sell them from that store again.)

5.
the "armour" is a cheap paintball "chest protector". I got it as a cheap option (since i was buying their urban camo overall and had to pay shipping anyways) until I make up my mind about what kind of armor I should get.
They have various options for a "chest protector":  https://www.paintballshop.cz/en/scripts/hledej.php?rz=1&retezec=chest
I went with the "PBS Chest Protector (Woodland/Black)", (I painted the white text on it with a black marker pen,)
but I have in mind getting a more fitting chest armour/protector later on, maybe an expensive one.
I saw now that this website has in store atm a pretty cheap option for pouches around the waist that might be nice.
https://www.paintballshop.cz/en/military/gfc-molle-chest-rig-vest-ak-olive

6.
Urban camo overall. Cheap option (if you live in Europe).
(It could be better but more expensive, to get some good camo pants + light jacket/shirt.try to get the same (or at least similar) camo style for both the pants and the light jacket/shirt (with rolled up sleeves).)
https://www.paintballshop.cz/en/clothing/pbs-junior-overall-urban-camo
Size S should work if your total height is 170-175cm. If you are taller than that you will have to look elsewhere for the camo clothes because they don't seem to have bigger sizes atm.
(I cut off the wrist parts of my overall because the rubber bands in the wrist areas was uncomfortably tight, and I would keep my sleeves rolled up anyway (and the overall was cheap).) (It should be easy to use a stapler to secure these sleeves in a rolled up way if you don't feel like sewing.)
The neck part is foldable.
(There are buttons on the overall ankle parts that I pushed just below the upper lace parts of the boots, to make the ankle parts "hug" the boots a bit.)

7.
Police/security/military purpose boots. (Black)
I'm wearing HAIX BLACK EAGLE Athletic GTX mid/black boots.
You can get such boots on ebay (or perhaps a store near you):

https://www.ebay.com/itm/254103701983?var=553443309142&epid=15050823177&hash=item3b29c2c9df:g:cisAAOSw9jJjikdG&amdata=enc%3AAQAIAAABACTYM7pUdhH84jmj5yL21a7qfpZN4EiQDyGRTSL%2F29jDpq9Js7FenPoWIcJop2eWQf2uBqZpjU%2Bk0sFgPyMJW9qjmi6k4AWbL%2B6GgiGvebCgGHpB5M7U2xJu6%2FNCyhVxLQDYl27SH9xxC63teI2jU1OUCMr9KBRIoHS8UyJK3kj9lTC%2BncgYdrWLQdurBqpI%2FTuMBWBk6reNIxy%2F0oaFxNlK5UduaBDLCiQcbb7dzQt2n%2BOgyjavTKOPhDAwiRTNhjzCHEc4idvT%2BymZfKEEQKjhg%2FdQSmGAtY6TqXVaamPGEr5FCOLQhqChyY84TQXnwIWWOLsQyIOsez5HaNKUz%2BM%3D%7Ctkp%3ABk9SR8rt-cHXYg
though I think HAIX BLACK EAGLE Athletic 2.1 GTX high/black would fit specifically HECU better! (because of them being high.)so, these then: https://www.ebay.com/itm/385736861728?hash=item59cfb56820:g:nhEAAOSw8Q5kptx6&amdata=enc%3AAQAIAAABAAUYew960d%2F7jwb8euHIUKrHQwgl3wbVOwvoPiDrhRyVcpDRrzSojrEabK6Sh6ysCTh37vyXtQ0v8atH0keoFjcZHz4PuL%2FRCged49kkRYaLdv8eTLVIbjM2jOCXEGXb2y6vhzlahFty4CVixVkJYCAFKENZNYeAn%2Bk5QNAjrYvhmvUVwx5GIuYkQKUROoeASK8equ8B4vwctP6QSS4EHeIDhuhwFyIW0HEItqE4lL0mNjHsGa2hw7Om8jHzAmmhVqg6KA1IYfafEbgtzssk%2BFNefREuVKiF%2BbJMD0y2553HS%2FmwjM5H63ucoMrnUhWQQBfs8A9dsnBUNIp9Pa4n9mo%3D%7Ctkp%3ABk9SR4qD19rXYg

8.
Smartphone attached to the ALICE pack shoulder strap
with the help of the smaller part of this lanyard https://www.jula.se/catalog/hem-och-hushall/kontor/kontorsmaterial/pennor/nyckelband-009635/
and a phone-wallet (+ small black rubber-bands).
(the lanyard attaches very nicely to the ALICE pack shoulder strap and locks it!)
the smartphone is in a phone-wallet, and I use small black rubber-bands to keep the phone-wallet from flapping.
I also have a second attachment for the phone-wallet that I attach to my waist rig-parts. I cut 2 small lines in the phone wallet to be able to have a carabiner clip (or something) keep the phone towards the torso so it wont be flying around much.
I have an edited picture of a Baofeng UV-5R (a communication device that looks a bit similar to a HECU one) on display on the phone.

9.
Fingerless biker gloves (with holes for knuckles)
https://iswag.se/produkt/unisex-punk-gloves-laderhandskar/
these will probably be too small for you if your hand size is bigger than medium size. (there is only one size unfortunately). Will probably fit nicely if your hand size is medium or small.
(if your hands are a bit too big for those gloves, then these might work:
https://iswag.se/produkt/laderhandskar-utan-fingrar-for-kvinnor/
they are slightly bigger.)

10.
(UK) Military bag for helmet (that has space for the gas mask).
Got mine with the S10 gas mask I bought on Ebay.
I attached it to the rig-parts around my waist.
You could option for a gas mask bag or such.
There are also a variety of waist bags here:
https://www.tacticalgeartrade.com/tactical-gear/bag-case/waist-bag.html

11.
Drop leg pistol holster (+pockets) ("Universal holster suitable for most pistol frames".) (black)
https://www.tacticalgeartrade.com/component-molle-drop-leg-pistol-holster-black.html
This is for the right leg.
(for the spontaneous pics I had already attached the helmet bag on the right side, and I didn't bother to switch side when i wanted to put on the pistol holster as well, so I put it on the left leg (just to get an idea of how it would look if it was a left-side holster) since they were just unplanned quick pics anyway.)
(also, HECU is seen wearing the communication device on the left side rather than the right side so you might wanna go with that.)

12.
also I'm wearing a black shotgunner/massn-style balaclava around my neck.
I'm having thoughts of getting an abseil harness. (It's a bit pricey though (and not sure if I should get a green or black one).)
finally, if not holding a military (replica) weapon, then a red pipe wrench would work as an iconic improvised weapon.(didn't have one at the time so I picked up a hammer instead.)