How about running across one of these?
http://arduiniana.org/projects/the-reve ... he-puzzle/
Basically, the link is a "reverse geocache" the box only opens when the box is in the correct geographic area by utilizing some micro-controllers and a gps chip. I think it would be super cool to make a traveling travel bug geocache that worked on the same principle. It would first be loaded with all of the current AR caches, then some swag placed in it and shut....once shut it can not be opened until the box is taken to the coordinates/cache it tells you...which happens to be a random cache location of the correct size for it to fit in. The parts to make something like this would be total about 60 bucks, minus the enclosure of choice, but it would leave a cacher talking about it for months more than likely. One could easily put a charge port on it allowing the cacher who posses it to plug it in an outlet to charge it up.
here is another one for the geeks out there...so who's going to make one?
I don't know what happened to it, but there was another thread very recently about this same "reverse geocache". might check into it..... it is a very ingenious piece of work.