I would possess Charlize Theron's body, slap Keanu Reeves and break up with him, and then return to my own body to try and score with Charlize Theron.
If that's not possible, I would possess Michael Moore's body and eat an exploding Twinky.
If that's not possible, I would possess Amanda Tapping's body and turn around in a mirror to find out what her butt actually looks like, because you really can't figure it out by watching every episode of Stargate and Sanctuary. After that I would feed her dog because he'd be looking at me with those sad eyes and a quizical expression because Amanda probably doesn't waste too much time staring at her own butt. I know I don't.
If that's not possible I would possess the body of Betty White and go beat the snot out of Jesse James, for cheating on Sandra Bullock and divorcing Janine Lindemulder.
If that's not possible I would possess the body of John Gotti and go "Where the f*ck am I? Holy sh*t! I'm a skeleton! But wait. Where the f*ck am I?"
If that's not possible I would inhabit the body of my cat and finally put an end to the mouse's tyrannical occupation of wherever that mouse is this evening.
If that's not possible I would inhabit the body of Linday Lohan and get myself tested.