Mine? IT freezes time so I have enough thyme to do everything I want to do. I.E. all my coursework for the next few years, eat a few cows, play every game I ever wanted and get 1000 GS is all on the 360, and do enough work for a chosen company so that I can retire immediately. Also, get hired for the military for Black Ops type stuff.
I would also like to be able to go back in time to prevent game developers from releasing shitty games and ruining perfectly good franchises(Halo, for one. Sonic for another.).