Ok... I play RPG games (AD&D mostly). I'm a geek who likes knives. Don't laugh though... that is how the Jedi got started
I haven't had a group in awhile but I'm a once-and-future gamer, too. I have about six milk crates of out of print RPGs, mostly TSR but some other stuff. I have a ton of AD&D, 2E AD&D along with a bunch of original D&D stuff. My collection even contains some books autographed by Frank Mentzer! In my stuff you'll find nearly every orignal AD&D book plus multiple copies of almost everything 2E; this is because if I find potential players that don't have books I can provide them. So far I have 6 copies of the 2D players guide. Also most of the Dragonlance, some Dark Sun, Ravenloft and a ton of Spelljammer material. Beyond AD&D I have another game Gary Gygax created, too, as well as Rifts, Torg, GURPS, Warhammer, Warhammer 40k, Werewolf, etc. I also have hundreds of miniatures. Painting them was a big hobby of mine although I haven't done any in years. Since dice are part-and-parcel of RPG games I have a pretty extensive collection of dice (d4, d6, d8, d10, d20, d30 and a few really odd ones). At last count I had around 335 dice from Chessex and a few others. And I'm always on the lookout for more.
Comic book collecting was once a big deal for me. I still have my books but I haven't bought anything in awhile.
My most expensive hobby is audio. I suppose I've sunk about $13,000 into my current audio system and perhaps another $25,000 into various disc formats (from LP to CD to DVD-Audio and SACD). My main love is classical but, oddly, 80's heavy metal. When I buy new music these days I've been more into alt-country, jazz and other strange stuff.
Before you all think I'm the biggest dork ever to don a pocket protector, let me quickly point out that I also am very much into knives and guns!

Lots of JKs in my collection (by way of my late dad). My gun collection is mostly handguns and heavily biased towards HKs. I get out camping maybe 20 times a year, too.