I would spend my days and nights trying to turn it into billions and more billions and then even more billions.
The only down side I can see to having that much money, though, is that it would ruin my life. Suddenly I'd be important, valuable, worth something, be somebody, have power. It would be horrible. I'b be afraid to cross the street least I got runed over. I can't think of anything that would piss me off more than dying with 300 million in the bank.