Metal bottle caps. Like beer bottle caps. Started when Fallout 3 was out and never really stopped. I haven’t counted in a long time but I’d say it’s around 5000 or so now.
Different variants of Fight Club, mostly VHS, DVD and Blu-ray, not so much the book, although I do own a copy. I have one of the 500 Comi-Con 2014 Blu-rays they made. Have all the Fight Club 2 comics as well, even some rare cover variants.
Also Halo games and collectibles. All the legendary statues, limited edition versions, etc.