I use an artists A5 sketch book and pencil to plan for upcoming shoots. I sketch out individual frames of ideas to use as a guide on the day of the shoot. Some I end up using and some I don't. But I know that I have something that I can use if inspiration doesn't show up on cue!
Sometimes a sketch will springboard from the original idea into a completely different direction, but it gives me a starting point. I have a portrait shoot this weekend and the request is "black and white and unusual". I have a few sketches, I might use some none or all of them, but I know that I have ideas and somewhere to start. I'm also lucky enough to do whatever crazy ideas I come up with.