Garish hoodies, at the moment.
My latest addition to the collection is white, with purple unicorns and rainbows on it. It's nauseating and it's my new favourite thing ever (picture at yfrog.com/hs5tqpjj i can't post links yet).
I keep foreign currency from countries I've visited, too. Usually a low-denomination much-used note. And for some reason all my towels and bedsheets and cushions and stuff like that appear to be purple, but that more happened by accident. I'm not even overly fond of purple. I also keep old USB cables and chargers from gadgets that have long since died, figure they might come in useful someday. Sometimes they actually do, and that makes the draw of tangled wires totally worth it.
Went through the usual phases as a kid. Gel pens, marbles, pogs, Enid Blyton books, Parker fountain pens, trolls, stuff like that. Belts was an unusual one, it was the one bit of customisation of my school uniform I could get away with so I had lots of them. Used to do the comics thing too, but spent far too much money on them so just randomly stopped one day. Have lost most of this stuff over the course of many house moves over however many years it's been.