I only actually collect flashlights currently, around 75 at last count. By collect I mean in the technical sense of getting together specific stuff for a historical or interest reason.
I used to collect vintage computers and cameras. The computer thing sort of got out of control and then the bottom dropped out of the market, so I'm liquidating most of it and just keeping the most important ones. I just lost interest in the camera collection and I've been gradually selling it off.
Now, there's also stuff I accumulate because I'm interested in the field, but don't have any intentions of collecting it. One is hi-fi equipment--I'm always buying good deals on high-end (usually vintage) home audio that comes along, and seeing if it's better than what I already have. As a result I end up with a lot of gear I don't use. Recently been selling off the spares so I can reclaim some space.
Other interests that involve too much stuff are wood/metalworking machines and related tools and outdoor power equipment.