I would pay to be able to overhaul the agricultural system to get beef off the market so that we can instead grow vegetation to feed the planet, ending one of the worst things ever: hunger. I would then pay for water filtration plants in every state/country so everyone can be motivated to drink water instead of soda.
After that, I'll have done my part, and I'll continue towards my next goal: doing whatever the heck I want! Riding a pony in the meadow, ride my bike across America or maybe even go on a world tour around every continent (I would, of course, fly over the oceans on a plane), move to Ecuador and have my own house built, and study whatever I want. 🙂