See, I understand if you meant "how to spend it all on my desires for luxuries."
But if you truly meant "how to spend it all," I disagree with you. Every day, I think of a new company that would make the world a slightly better place. Every day, I wish I had 50 billion dollars so I could call my manager up, tell him "you have 3 million, find someone who can solve this problem," and have it done.
Hey, just building a worldwide cellphone network with enough bandwidth to not suck and decent international rates could take up more money than I could ever possibly earn.
Dream big.