Lately it's been audiophile stuff for me too: vinyl, turntables, speakers, amps, dacs, headphones....
Usually, though, it's movies. I'm a sucker for physical media and I like to own movie just for the artwork and special features. When a movie is only $10-$20, it's easy to just order one on impulse. Next thing you know, you've spent thousands of dollars on a movie collection of which you'll probably barely watch half of them ever.