From the wish-Id-thought-of-that department: the Flashbag. Its a standard USB flash drive that has a tiny pump in it that inflates when you load it with data. So if your drive is full of stuff, it blows up like a balloon, but if its empty it remains flat and rectangular. Itll stay inflated even when powered down, so youll be able to estimate how many more MP3s you can leech from your friends computer just by taking a gander.

Unfortunately, the Flashbag is merely a concept design and there are no plans at this time for it to be manufactured or sold. We hope some brave company will decide to start making them soon, for if theres anything the world needs, its more bizarre USB devices

[Via Plusminus Design]