Music, above and beyond everything else. I have tons of vinyl, Cd and digital music, been collecting since I was a child. Also books - I have a hard time getting rid of a book, even if I didn't like it and I would never destroy one, out of respect for the human thought and knowledge it represents. I also collect movies and am in the process of replacing a huge collection of Dvds with Blu Ray discs.
As a 20something, I used to collect a lot of unicorn bric-a-brac, until suddenly it became chic and I lost interest, not wanting to be involved in something common. Went through a period of obsession with collecting action figures for a few years, but I'm over it now. I do still collect Batman and Superman memorabilia and Betty Boop items, if they're unique enough. And radios, antique radios.
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"I don't mean to sound bitter, cynical or cruel - but I am, so that's how it comes out." - Bill Hicks