What a pleasant question to consider! Let's assume a big payoff -- like $100 million.
First and foremost, I would pay off my mortgage. It's a huge amount (to me) and I never want to think about it again.
Second, I would sock away substantial amounts for my kids' college and my retirement, plus a trust for my kids and their kids -- enough for comfort but not indolence. 20 years of living on the edge has made that kind of financial stability more alluring than Inuyasha in a loincloth.
Third, I would choose two main causes -- probably support for single mothers in the workforce and one form of medical research (such as pancreatic cancer, Crohn's or diabetes, all killers in my family) -- and develop significant philanthropic relationships with organizations that are making real progress in those areas.
Fourth, I would contribute to several other pet causes in my community-- thinking both local and global.
Fifth, I would do work on my house. I might move, but then again, I love it here, so I might rip the front off and give myself that dream kitchen, family room, fireplace and bathrooms I've always wanted. I'd also get the damn landscaping done already.
Sixth, I would buy a few toys, like a gorgeous, light laptop and a fun (but fuel efficient) car.
Seventh, I would plan 1-2 fabulous trips per year with my kids. Maybe one trip abroad, and summers at some wonderful shore location (like Greece. Bwah!).
Eighth, I would get a personal trainer to come whip my ass into shape with daily workouts, and a babysitter/driver to handle the incessant driving to and from school, skating, soccer, karate, etc.
Ninth, I would hand checks for, say, $50k each to everyone in my family and all my good friends.
Tenth, with all of that taken care of, I would shut myself in my studio and WRITE!
How about you?