Can't discard weapons at all, which goes back to my nitpick of not being able to manage what weapons I'm carrying. The game at some points kind of assumes that you're picking up every weapon available to you (and some are actually easy to miss if you play with UI off like I initially did). As a result, you have to carry every weapon, which makes more ammo types spawn, which means less space/chances for ammo you REALLY need at the moment. It was a bit annoying in the final campaign because
gets a lot of weapons, two of which have alternate ammo, and two of which burn through ammo quickly, so you usually carry 2 spaces worth to make up for it. The result is that I could never carry grenades and had to always throw stuff away to pick up/combine herbs because I was always full.
Something I read here did make me curious about alternate weapon locations though. Someone mentioned that the weapon you get in Chris chapter 2 (which is very missable) actually shows up again at a later point, which makes me wonder if the same applies to the other weapons in the game.
It's a small world after all!