Why uy a car when you can buy a zeppelin?
Anyway, I'd buy a lot of cars, trucks, tanks, helicopters...
And I'd hire a lot of minions to drive them. (And to take over the world.)
I'd also buy quite a bit of real-estate away from countries...
Maybe all of it...
EDIT: Thinking about it more logically, I wouldn't be able to buy anything with it because the inflation caused by there being an infinite amount of it would make it totally worthless.