In reply to jon:
Commonly, a waterproof plastic box with a logbook, a "stash note" (a card that explains what it is) and sometimes some swaps in, usually with "Geocache - contents harmless" written prominantly on the outside. However, it could also be:
- a tiny magnetic container the size of your fingertip
- a "bison" (small waterproof capsule)
- a film can (for cliche purposes, hidden in an ivy-covered tree)
- a fake rock
- a fake dog turd*
- a fake snail
- a fake leaf
- a drilled-out fir cone
. . . and anything else limited only by the owner's imagination. :
(*Ok, I'll admit it . . . I was the perpetrator in that case. Only had one find so far, I think I made have made the puzzle a bit too hard.)