"Este regalo no es tuyo" ("This gift ain't yours") is an interesting project-experiment by Honest&Smile; using 500 USB memory sticks as bottles of messages. Find one, grab a thing, add another of yours, leave the stick somewhere else and then tell your story in the wall of the Facebook page for the project:

Sponsored by a few brands, don't know what the outcome of this might be, but the organic nature of it made me curious about what people could trade.