In the location Asö, the middle storage crate has two look boxes. It’s tricky to get into, but if u do, it’s almost impossible to get out by normal means. I’ve only gotten out once normally and it took 30-45 minutes.
Yeah be careful going into those crates, from what i’ve read in past posts the devs are working on it. My rule of thumb is if it looks too tight dont go in. Hell ive gotten stuck under a cars trunk hatch. There is plenty of other places to look for supplies.
It’s also good practice to keep a field radio with you at all times to be able to un-stuck yourself. Or just fast travel to the nearest safe house. There are quite a few opportunities to get stuck in this game, although not as many as you might expect from the vastness of the environment and the otherwise overall game state.
How long into doing this it it take for you to realize it would have been faster to fast travel to a safe house and run back? 
Great job on not giving up though 