My gran once received a box of plums sent by some old wifie. They were totally rotten and weeping by the time they arrived.
My friend's brother sent him a dead squirrel in a Pringles tube.
Not sure I have received anything that interesting. A picture of Eoghan Quigg, or a giraffe posing pouch found on the floor are probably the only unusual things. Oh and several pictures of a woman I didn't know receiving a massage, but I don't think they were intended for my address.
I like the tale of that man who sent himself in the post, to try and rob the post office. Not convinced it actually happened though.