When Marianne is waiting for Professor Sutwell to return from the beach, she listens to a record album. The label on the record is from 'American International Records', a reference to the production company that made the movie.
At the end when Von Zipper says "I will return!" to the beach gang, it's still daylight. But seconds before, the gang is gathered around a campfire and it's pitch dark.
Early in the film, when Frankie and Delores drive onto the beach towards their beach house for the first time, there's already a set of tire tracks in the sand from a previous take.