Acting for Two: Jonathan Hyde plays both Alan's father and Van Pelt. A common theory is that Jumanji conjures up Van Pelt by taking the form of the person you had dreaded the most, and for Alan, it's his father—especially since Van Pelt spouts out the same criticism as his father.
Jonathan Hyde playing both Van Pelt and Alan's father could be one to Robin Williams' role as Peter Pan in Hook, as most theatrical productions of Peter Pan have Wendy's father and Hook played by the same person.
Defictionalization: A Jumanji board game was released when the movie came out. It shared many elements with the game in the movie, aside from the supernatural elements, like the automatically moving pieces or sucking in players...we think. It also used cards, not even attempting to copy the magic-8 ball style interface. It came full-circle again when Zathura came out, which used cards. Returned to shelves in 2017, when Cardinal Games picked up the license from Hasbro.
The novelization contains an explanation for why Nora had to talk with the principal after Peter and Judy's first day: the realtor's son called Judy out on her lies, and Peter started a fight with him.
The 2017 Blu-ray release revealed that Carl eventually became the president of Parrish Shoes. Also, the Christmas gifts Alan gave to Peter and Judy were pairs of sneakers inspired by the game, complete with Jumanji imprinted on the bottoms.
Enforced Method Acting: Robin Williams admitted that he did not need to act startled for the scene where Van Pelt is shooting at him, as the blank gunfire was extremely loud on-set.
Fake American: Australian-born Jonathan Hyde plays Sam Parrish and Van Pelt. He uses a slightly American-sounding voice as Sam, but gives Van Pelt an English accent.
Font Anachronism: The typeface used for the board game Clue came out only in the 1990s.
The gun shop owner asking Van Pelt if he's a postal worker. Around the time of the movie, there had been a lot of news stories about postal workers going crazy and shooting up their workplaces, from which we get the expression "Going Postal."
Robin Williams noted the parallels of Alan and his father's relationship to his own father's with his grandfather.
Alan advising everyone to get to higher ground when the monsoon hits. In a jungle, dense rainfall and heavy humidity can rot human flesh very quickly, so this is pretty apt advice.
It was indeed a crocodile that Alan wrestled for Sarah.
Technology Marches On: Referenced when they start playing the game in 1969, with Sarah remarking that the self-moving pieces must be done with magnets. When the kids continue the game in 1995, Judy suggests it's done with microchips, which actually makes less sense. Plus, Carl proudly showing off his prototype for a modern basketball shoe.
Trolling Creator: Robin Williams would often give fake answers to people who asked him what the title meant. "I tell them it's an island in the Caribbean. Book your travel there early".
Unintentional Period Piece: To the point where it was lampshaded in the sequel. The idea of a cursed board game causing havoc to those who play it dates the film to before video games fully displaced board games as the group "play" activity of choice among kids, a point raised in the prologue to the sequel when Alex decides to pass on playing it in favor of his video games — causing the board game to transform into a video game cartridge instead.
In earlier drafts of the films, Nora was supposed to be Judy and Peter's mother.
Alan's parents wanted to send him to boarding school for a different (and better) reason than in the final draft. After Alan was beaten up by Billy Jessup and his gang, Alan's parents finally realized that Alan was not fitting in with the other children in Brantford, correctly guessing that it was because they were jealous of Alan's wealth and status as a Parrish. Therefore, they believed he would fit in better with boys at Cliffside (or "Boden" as it was called in the original draft) because they were more "his status." The end result was still the same with Alan though.
In the original draft of the film, after being turned into a monkey, Peter slowly regressed to Hulk Speak, and lost his memory of being human and whatnot.