It is fun to watch the movie, therefore, plan on going for a night you like that movie.
S'mores kits are about $2 and outfit 2 people. They have inexpensive snacks & hotdogs, too.
The movie schedule is posted on the 1st day of each month over on the Camping Board. It is not available prior to that (anywhere).
Depending on where you are staying/coming from, it is fun to ride the boat over to FW. You might also want to visit the petting zoo, but that closes a little earlier.
Depending on the time of year, the movie might be "late". We like to go when we don't have an early morning the following day.