I love them for mini collages, collage the inside and top off with ultra thick embossing powder (clear). Place on a pan over the stove, with decent heat. After melted let cool and add another layer and repeat.
Use in larger collage pieces/shrines, superglue magnets or pushpins to the back, drill a hole at top and make charm for necklace or earrings. Or just drill holes in them plain and use as earrings, I bartend - customers always get a kick out of it.