I collect bottle caps from many kinds of drinks (beer, soda, radler, et cetera)
Coz it's fun, also caps (especially beer ones) are plentiful around here and I'm a Fallout fan (only played NV but it was amazing, fanboys can fizz off).
I also like to joke that these are gonna be the next currency when the apocalypse (eventually) happens but of course they'll be worthless (too easy to counterfeit and so on).
I just keep them in a bucket in my room, here's a pic: