Well, people get a container and put stuff in it and then hide it somewhere and then post the coordinates online. Then you, armed with your gps enabled device go, and find it. They have them all over the world.
My gps enabled device tells me it's in here
Look at all the cool stuff in there.
OH GOD A POORLY PHOTOSHOPPED DINOSAUR!
WTF WHY DOES IT HAVE LAZER BEAM EYES!?