Cormac McCarthy appears to be an exceptional case in this respect. I skimmed through a book about it once. Early on he basically earned his keep through grants and book sales. I think he persuaded one of his old ladies to get a job while he wrote. And apparently he was always writing; pitching one book in the middle of working on another. I guess film and television soon followed.

Most of the jobs listed seem something you can do on autopilot, while your mind is doing something else, which would make sense for creative minds.