I keep some unwanted items as things to put on pressure plates (so I don't have to use rocks/missile weapons) and as breadcrumb markers so I don't get too confused about where I was vs. where I want to go. Haven't had much issue with inventory size.

But yeah...I wish a few more things stacked, especially torches.

you know, I got to a point where obsessive hoarding was ruining the gameplay.
I was constantly overburdened, chucking crates and pouches, smack-full of total crap in front of me everywhere I went.

Torches? Bring tops 3 of them with you at all times.
If you have old gear lying around for that off-chance that you might find useful later - just get rid of it, you'll thank me later.

***minor spoiler*** And all those pesky notes (a few exceptions ofc) - If you found no environmental use for them on the level you picked them up, fraps screenshots or write them down then leave them behind for the next guy that walks by and has to take a crap.

As for mortar, ingridients and bombs, use them - if you don't they will pile up real quick on you. oh and running around witha stack of 20kg stones for pressure plates isn't very fruitful. Use torches. Or throwing knives.
***end spoiler***