It's a fascinating question, but let's just start with the assumption that I get a few billion and the tax man takes half. I have 1.5 billion to work with.
I'd probably start out with setting up a few small charitable trusts with 10 million each, for things that I care about in my community -- food banks, educational assistance for economically disadvantaged students, and housing & heating assistance for the elderly and disabled. They would pay out 5% of invested holdings every year. This would get me on a nice dinner party schedule, with some benefits to attend and give me some causes to work on and with other like-minded people. It doesn't have to be flashy, but it does have to be meaningful to me. This is how I'd meet people and pick up a social life.
I'd build a new house up in the mountains, with room for all my toys. I'd get an apartment in NYC and another house out in southern California. I'd probably move around between all three, through the year. I'd probably do a fair amount of traveling abroad as I felt the need.
I suppose, if my GF didn't care for this life, at some point I'd meet someone that would want to go along for the ride.
Honestly, I'd park most of the money in cash and securities and play it by ear.