According to Sean Astin, he was allowed to keep the treasure map used in the film. Several years later his mother Patty Duke discovered it, thought it was just a crinkled piece of paper, and threw it in the bin.
(at around 46 mins) When the Fratelli brothers argued, Anne Ramsey really slapped Robert Davi. She was told to hit him as hard as she could.
The pirate ship was entirely real. All the shots were filmed in the ship. After the film, it was offered to anyone who would take it. No one wanted it, so the ship was scrapped.
The cast was not allowed to see the pirate ship before the scene was shot, as director Richard Donner wanted to catch their genuine reactions at the size and scope of it. When they did see it, Josh Brolin was so surprised that he exclaimed "Fuck!" The scene had to be reshot.
Mostly shot in sequence. Total production took five months.
Jennie Lew Tugend: (at around 1h 40 mins) assistant to director Richard Donner, has a small role as Data's mom.