Personally...
1. Buy Fire Truck
2. Drive said Fire Truck around places
3. Buy Ford GT
4. Buy maxed out PowerMac (MacMac) and MacBook (pro) and get my damn iMac delivered before the 2nd Feb!

5. Contract Jonathon Ives for development/creation of iTablet
6. Buy Time Machine
7. Use said time machine to travel back to 2000
8. Whilst in the year 2000 buy LOTS of Apple Stock
9. Use my now [2005] $20Bn (approx) to invest, spend on charities
10. New York Penthouse, Edinburgh Penthouse, Sydney Penthouse...Actually...I'd buy New York, Edinburgh and Sydney. Outright. Bang.
11. Buy a fussball table
12. Rennovate my school - Replacing all (and I mean ALL) of the computers in said school with maxed out macs.
All done I think