Excerpt from Through the Tollbooth:
I don’t think anyone will ever be able to adequately explain where story ideas come from, but for me, they usually arrive when I’m standing at the kitchen counter eating crackers out of the box and letting my mind wander all over the place. As it wanders, it stumbles over a strange or silly thought, and I sort of laugh to myself and say (with a mouth full of crackers), “That would be a good idea for a story.”
Usually, it is not a good idea for a story.
For the full, read here.