I missed this discussion when it first came up. I think I suffer from "pack rat" syndrome as I seem to "collect" all kinds of stuff. As to things I actually put effort into collecting there are coins (an uncle got me started on those when I was a kid giving me coins for my birthday and Christmas), cartridges and old ammo boxes that are my main interest other than guns. I have collected a lot of books (mainly military and guns) and old gun magazines, binoculars, various militaria and old hand tools. Don't want to think about all the odds and ends of old stuff I have stashed away over the years just because they were interesting.
Never know what I am liable to add to the mess, even my gun collecting has taken off on different courses over time. I have put together several collections with different themes then sold them as I went off on a tangent to collect some other type of gun in it's place ( I would have had to be really well off to have kept them all anyway, oh well, that's life!).