I usually just mill around the convention halls, posing for pictures when asked, and asking others to pose for pictures I'd like to take of them.
I'll attend panels if I see anything interesting, though the past two years KumoriCon hasn't really had many panels I found all that interesting (some voice acting panels last year, a Robotech panel the year before, can't remember what else I've been to).
I don't have any friends to hang around conventions with so that's out, though I wish I did, it'd be fun to have someone to hang around with rather than wandering around by myself.
I do try to pick up a keychain whenever possible as I collect them. I also try to find at least one Gundam model whenever I'm at Kcon, though last year I didn't buy one as I really didn't find many Gundam models at all. Weird.
But I made up for the lack of models there by buying them at HLJ.com. XD