Great thread. I've been thinking about this a lot lately as the holiday season (aka gift-getting time) approaches, and I look around my very small apartment at all the STUFF. Mostly, they are things I really like and want, and will in fact use someday, but I honestly don't need to have THAT much stored up in advance. Books, blank notebooks, craft supplies, DVDs, magazines, etc.. So that's a case where I need to use what I have already, and stop acquiring more until I get a little ahead of the game.
Sometimes I keep stuff because it made sense at the time (years ago) to keep it; and now, I
could get rid of it, but that would involve digging out the storage containers from where I've so expertly tucked them. Kind of bizarre, now that I think about it--I use those places to store things that I really want to hang on to, but they're so inaccessible, I can't use them to store anything I'll actually want to
use anytime soon.

Sometimes I feel bad just chucking something in the trash because I think, "Surely someone could use this!" But am I really going to go to the work of finding that person? Gently used clothes are pretty easy to donate, but what about textbooks from ten years ago? I feel bad throwing a book in the trash, but I know I'm never going to read it again, and it's probably at least a couple editions behind whatever the class requires today.
Also my dad's family are hoarders/keepers. Any space my dad gets fills up with junk mail and the like that he
just can't part with. It is a deep-seated emotional thing, almost a phobia or anxiety--my dad is so nice and mild-mannered and easy-going, but if you threaten to throw out one plastic sack of ten-year-old grocery store sales fliers he just morphs into this entirely different, angry person. If he sits down and takes the time to go through the sack, he'll end up throwing out some (but not all) of it, but even doing that is visibly hard for him. His siblings are like this too. The worst part is that they don't actually take care of stuff--they'll always say, "Oh, keep that, we might need it later," but then when they really
do need it, they either can't find the thing in the mess, or it's broken and useless because it was just at the bottom of a pile somewhere instead of really stored. Seeing this kind of thing is what really causes me to constantly rethink my stuff, look for whatever small amount I can get rid of, make sure I'm storing things properly so I can find them and use them if necessary, etc..
Perhaps oddly, I don't really attach much significance to gifts in particular. I love to get (and give) gifts, but I can throw something in the trash as soon as I get home, or regift it, and still think warmly about the person who gave it to me. I don't get much in the way of home decor, clothes, etc.--it's more like books, and I will cheerfully say I haven't read it yet if someone asks.