This one is hard. I could be the POTUS for a day, but I doubt I'd do a better job. Actually, I'd probly be terrible. I could be a supreme court justice on an important day and switch their vote... those are all useful ones. Or something useless. I could be a bird for a day, and feel what it's like to fly. Or a whale, and feel all huge and powerful in the water. Or, if this is really broad, I could just be an invisible person of me anywhere in the world, and follow someone around and tickle them when no one was around. That last one might be a little evil, tho. Hard question.
What would you do if an alien offered you a one way trip across the galaxy, but you could only bring one other human along for the ride?