After I've gone and got all of the stupid out of my system (i.e. jump into the Grand Canyon without a parachute, play hot potato with a grenade, brush my teeth with nerve gas, etc.), I'd spend some time going to business school while also studying computer science and engineering. I'd use my knowledge to experiment with various business ventures before eventually landing myself a very lucrative company to amass capital for my "dicking around" fund. After that, I'd spend my seemingly infinite time and fortune doing whatever I want, learning everything I could, and possibly engaging in a few side projects (like choosing a group of newly orphaned infants and engaging them in a life long social experiment where I place them in various social, economical, and educational climates and see how they develop/what they achieve).
Don't get me wrong, I wouldn't just spend my life goofing off. I'd build an empire with my financial resources in multiple fields, be it pharmacy, electronics, alternative power, weapons, etc. With enough time (and luck) on my side, I could probably subtly steer the advancement of mankind in whatever direction I choose. I might even be able to control the domestic and foreign policies of entire countries with enough resources at my disposal. Ultimately though, I'd probably expand into terraforming other planets for colonization once I've depleted Earth's resources/overpopulation. Who knows, maybe I'll start a galactic civil war like in Firefly while I'm at it?
Edit: Now that I think about it, discovering time travel while I'm at it would open a whole NEW field of dicking around when I bend the time stream over a pinball table.