Be as thin as I possibly can! Why? Because I could.
I'd do dressage. Why? I love dressage.
I'd be a ballet dancer. Why? I love ballet and I wish I could be a ballet dancer.
I'd apply at my dream university and go there. Then work for something like National Geographic and travel the world. And then dazzle some tall, dark, and handsome man, fall in love, get married, BOOM, happiness achieved.
Lol, this scenario probably only works for one thing doesn't it? If I had to choose between the stuff above, I'd go to a great school and get awesome grades, thus preparing myself for my dream career and dream man
I'd become a professional football ('soccer') player.
There's plenty of things that I dream of or that I'd love to try, but I'm quite confident the above would be my first choice. There's nothing like being out on the field.
Build a starship with a FTL drive that's able to ignore the laws of relativity.
Why: Earth isn't even a speck within the universe and there are far too many cool things out there that need to be seen in person rather than through a telescope.
insure that people in all parts of the world have a safe and healthy supply of water and food that is enough to keep them alive, healthy, productive, and generally happy.
Save every child in this world from emotional despear, make them feel loved and cared for and give them everything they need. Plus teach them how to be successful. All in all save the world form it's self.