I would invent a teleporter or something like that. Not necessarily like Star Trek though.
God there have been so many times that I've wanted something like that, especially in the last year, It would make life so much simpler. Hell it might even help with the environment, because you wouldn't have to use as much fuel to get somewhere.
This is probably some idealistic crap that I certainly won't be able to invent.
But maybe... Just maybe someday one of my crazy smart friends who's going to Berkeley will invent one.