I think it's in my genes to collect or hold onto things that I probably have no use for. For example, I collect matchbooks whenever I'm out somewhere, though I rarely use them for anything since I don't smoke & don't burn incense or candles very often. I just think they're neat since they're little pieces of design. :)
I've also been collecting vintage suitcases in hopes that one day I will find a use to make out of them. I've wanted to paint/decorate them and maybe resell them. I also found that really cool website where someone made amps/speaker boxes out of them.
I also collect cool/interesting event flyers. Working at a print shop, I print out a lot of flyers for different people. I usually make myself an extra copy if I especially like the design. I've collected so many and I've been meaning to put them up on my wall in some decorative fashion. I've only managed to hang up a couple though.
Another thing I collect is business cards. As with flyers and matchbooks, they are another form of design and I like to keep ones that I find attractive.