(NSFW) Have you ever used a body cavity as a place of storage?

OK – I’ve seen these TV shows about the harsh realities of prison life, and one thing that really trips me out is how these guys will store shanks in their bums (presumably wrapped in plastic or paper to avoid internal injury) for later use – ouch! Does anyone else remember the part in Jackass when the dude put a toy car up his rectum?
Also, I have a friend that once stored acid in her vagina in order to transport it back to the States undetected (according to her the European stuff is superior to domestic varieties).
So this got me thinking, how common might this practice be? Does anyone here have experience with this, and if so, what were the circumstances?