Ah, the wonders of 3D printing. Here are some real-life Mann Co. keys, printed by Reddit user ikonakona. You know, the things you need to open up those pesky crates in Team Fortress 2?
Sure, you can't do anything with them, but still -- neat thing to have on your keychain. See, for instance:
Though if you really wanted you could probably print the lock used in the game, put it around a crate, and stuff the crate with hats.
Real life Mann Co. Keys - 3D printed [ikonakona]