In "The Terminator", Kyle Reese could have brought back a weapon from the future - by shoving it up his butt.

Dr. Silberman: Ray guns. Show me a piece of future technology.

Reese: You go naked. Something about the field generated by a living organism. Nothing dead will go. I didn't build the fucking thing.

Dr. Silberman: OK, OK. But this cyborg, if it's metal... ?

Reese: Surrounded by living tissue.

Dr. Silberman: Oh, right.