A lot of things really. Most of my game collection is in fairly good condition and I tend to buy games with the full packaging when I can help it. What often surprises me the most is how expensive guides are getting as I have the original Chrono Trigger strategy guide and I think it goes for more than the game these days. I also still have my cloth map for FFVIII and the Music Selection OST for Chrono Cross and FFIX. Not sure if some of it would be considered mint condition as I use everything I have, but I keep most of my games in nearly perfect condition. I may not have the true rares of gaming, but I have enough of the popular ones in good enough condition that I could probably get a really good deal for all of it if I had to.

Probably my most amusing rare memorabilia is my VHS copy of Final Fantasy: Legend of the Crystals including the special phone cards that come with it. I don't think it's worth a whole lot at the moment, but the series never got a re-issue or converted to DVD so it's pretty rare. I may need to take another dive in to see if I have anything really worth anything.