Something provisional is temporary, in the sense that it's only valid for a while. You'll often hear provisional used to describe things such as governments, elections, contracts, and agreements, all of which can change into something permanent.
People who go camping take provisions, which means supplies for the trip. This can be helpful when you're trying to use provisional properly. Remember that those provisions are, well, provisional—they're only supposed to last until the campers get home, where the real food is waiting. If you're in a rush to start filming, you might consider giving your star a provisional contract, so that you can at least get started. You'll have time to replace the provisional one with a permanent one while you film.