Tomorrow you get to live the day as anyone you want. Who'd you choose?
And no you can't just use the experience to buy your current self a bunch of stuff so you get to have it after tomorrow. It's about having the experience of living someone's life for a day.
Serious answer: I'd like to pick someone that would help change my world view after that day is over. The classic, 'walking in another's shoes'.
I'd take a nation leader. US President for a day or the Pope seems obvious but I'd really like to know if it IS good to be the king. Carl XVI Gustaf of Sweden. I'm going with that one.