I collect ephemera. Weirder the better, and I try not to ever pay money for any of it, so I have two scrapbooks full of weird notes, pictures, postcards, and other things.
Among my favorites are a school detention slip from the 1920's I found in an old book, some photos from India of two guys dressed like mods in a jeep, hand decorated envelopes (talking unicorns, spiders and glitter) some squatter left in an abandoned textile mill, and a scary tintype of an old woman found in an abandoned house.