Hmm...I'm torn between the apocalypse blade, the sonic screwdriver, the omni-wrench, or sly cooper's cane. Probably the wrench because its a lethal weapon and a tool. And I can lift it.
Also, if you are unsure of what any of these things are, you fail at life. Go look them up, better yet look up the show/games they came from.
EDIT: I can't believe I forgot about Ezio Auditore's dual bladed bracers. I'd like a pair. Not necessarily to use, but just to see how the mechanism works.