The film was originally slated to have a follow-up taking place in the old west and have an adventure inspired by Disney's Thunder Mountain and Phantom Manor attractions, hence Ezra's reference at the end to "the Frontierlands".
The Gypsy they trio is trying to get to is a reference to Madame Leota.
In the scene where the Carnie is introduced for the first time, there is a cutaway shot of a hatbox sitting in his office. This was added as a reference to the famous Hatbox Ghost animatronic from the Haunted Mansion attraction on which the film is based.
The film itself is loosely based on the characters of the Highhiking Ghosts from Disney's Haunted Mansion attraction, while these characters were never officially named, cast members and fans over the decades have them the names of Phineas, Ezra, and Gus.