To be honest, I have too many ideas. The good thing about my job as a freelancer is that I pretty much have as much freedom to go places and do things as I could want or need. The bad news is that I really don't take advantage of this, because as awesome as working on a beach in Barbados or in an Italian cafe sounds, plane tickets ain't free. But let's assume for a few minutes that money is no object. I would consider doing lots of things.
I'd go live in a country like Spain or Italy or Portugal and soak up as much of the culture and environment and language as possible.
I'd drive from state to state until I'd knocked all the states off my Life List. There are plenty of adventures to be had in my own country! (I've already been to Hawaii, so it's good I wouldn't have to drive there, heh.)
I'd go to culinary school. Just because I like cooking and I would love to improve my skills and be more confident overall.
I'd go somewhere secluded and beautiful, and just write. Maybe the next great American novel. Maybe my memoirs. Maybe just miles and miles of lists. (Hey, I yam what I yam!)
What would you do with three months?