Hmm.. cant say I really collect anything, I tend to go headfirst into any hobby I'm interested in and "collect" until I figure out exactly what I want.
Cars - I do a few track days a year, but no longer own a car for it. At one time I had 7 "racecars"
Motorcycles, still ride sparingly, but with kids, not so easy for wife and I to ride, so back burner. Once had 6. Now 3.
Cigars. A current exploration, but tapering down now that I've found what I like.
Guns. Never really cared for true collectable models, though I own some vintage Colts, more or less cleared out most of the ones I dont use regularly.
Beer. Was once a big hobby of mine, seeking out and collecting some rare htf brews, but got more into homebrewing and just make something similar for less.
I can't say there's anything I really collect simply for the purpose of collecting/having. But any hobby I get interested in, I explore all corners, then narrow down, and trim the collection.
I think the only things I buy without practical use, simply for acquisition and accumulation would be LEGO sets. But again, not necessarily the collectable items, just stuff I think is neat