I haven't seen many real-world use reviews of this pack anywhere online, so I figure I'll put up a post about it here after taking it out on a wet and snowy day hike to Annette Lake.

These packs are cheap, going for anywhere from $10-20 online, and almost all of them are in extremely good to unused condition. They're spacious (~50 liters), waterproof, and feature internal pockets for organizing gear, and have straps on top for lashing gear to outside of the pack. You could also probably figure out a way to attach something to the bottom of the pack too with some knotwork. The inside of the pack is comprised of a big main pocket, two sleeves on each side of the pack that could each fit a 2L bottle and a bit more, and two small pockets that are actually part of the top side flaps. I was able to carry an extra set of base layer clothes, a rain jacket, fleece, puffy jacket, emergency poncho/shelter, folding foam sit pad, two 1qt USGI canteens (one of which had a hydration hose attached to it) and metal canteen cup, small gas canister and stove, major and minor first aid kits, microspikes, some trail mix and an MRE entree. That filled the pack up to the rim, but I could have used the top flap lid to secure a sleeping pad, bedroll, shelter, etc, as well as secured something on top of the lid using the loops stitched on there. My load weighed probably about 20-25 lbs, and was relatively comfortable to carry for the roughly 8-mile hike using the Y-harness that came with the pack.

There are some things that kinda suck about the pack though:
1) It has no frame or stiffener of any sort. I made my own stiffener by cutting out 2 cardboard squares, aligning them so their grains were perpendicular, and wrapping them in duct tape. That did the trick and really gave the pack some form. Alternatively, you could also attach this pack to an Alice frame or some other sort of frame without much difficulty.
2) This pack would be really uncomfortable/unbearable to use without the Czech Y-harness. Some websites sell this pack without the Y-harness, so just be mindful of that if you decide to buy.
3) There are no external pockets of any sort, so you have to open up the main flap to get to any items you're carrying in the pack.
4) The sliders used to open and close the pack aren't as convenient as modern buckles, and can be kinda difficult to work with gloved/cold hands

Overall though, especially when you consider the price, it's a fantastic pack. I'll definitely use it on more winter dayhikes or warm-weather overnighters.

A pic of the pack after I finished my hike. All my gear inside stayed dry.

Where did you buy?

I got mine through Swisslink for $17. It's a few bucks cheaper on other sites, but adding it onto my order qualified it for free shipping and that made it worth it.

I found it for $13 on Coleman's Surplus: https://colemans.com/czech-military-m85-backpack

Looks like you might be able to get it tomorrow for 20% off for Cyber Monday sale. No idea what shipping is, I haven't found a place to estimate it without filing out a form to update their database.

EDIT: Found the shipping estimate, you can have it shipped to your door for the low-low price of about double what the ruck costs, or roughly 5x what it costs if you're in a hurry. Guess I don't need one that bad.