$10: I'd buy myself a nice hot taco.
$100: More tacos. Perhaps a soda, too.
$10,000: Probably invest in something. Maybe time travel, so that I could, some day, in the future, go back in time and tell myself to not to invest in time travel.
$1,000,000: Build the largest laser-tag pavilion in the world, maybe launching it into space to that it could be it's own planet, called Lasearth.
$6,000,000,000. Give everybody in the world a dollar. Personally.
I'd be like the anti-that-one-guy-in-hitch-hiker's-guide-to-the-galaxy-who-time-travels-around-insulting-everybody.
$6,000,000,010: Same, only with a few more tacos involved.