Kiefer Sutherland claimed in an interview that in one of the locations of the film, a Renaissance Fair was being held and the cast and crew attended and bought some cookies. Unfortunately, the cookies turned out to be pot cookies and two hours later, the crew found Jerry O'Connell crying and high on the cookies somewhere in the park.
The pond the boys fall into was a man made pool because the crew wanted them to be "safe and secure" and didn't want to put them a real pond because they didn't know what would be in it. But Corey Feldman stated in a interview the joke of the whole thing was they built and filled it with water in the beginning of June and by time they got to film the scene it was in the end of August. So it been out in the woods for 3 month and they didn't know what was in it anyway.
River Phoenix, Corey Feldman, Wil Wheaton and Jerry O'Connell got up to much mischief in the hotel they were staying in during filming. This included throwing all the pool side furniture into the pool, Wheaton fixing video games in the lobby so they could play them for free and Phoenix (spurred on by the other boys) unknowingly covering Kiefer Sutherland's car in mud; only discovering whose car it was when Sutherland confronted a scared and nervous Phoenix about it later.
According to Wil Wheaton on the DVD documentary, the scene in which Verne (Jerry O'Connell) can't remember the "secret knock" to the clubhouse was thought of by Wheaton, Phoenix, and Feldman on the day it was shot as another way to make Verne look more pathetic.
In the campfire scene in which Chris breaks down, Reiner was sure River Phoenix could do better. He asked him to think of a time in his own life when an adult had let him down and use it in the scene, which Phoenix did. Upset and crying, he had to be comforted by the director afterwards. The result of Phoenix's exercise is the scene that ended up in the final cut.
As with most of Stephen King's stories, this one originally contained connections to other books he has written. Ace Merrill later re-appeared in the book Needful Things (1993), although he does not appear in the film. The dog Chopper is compared to Cujo (1983). Characters are familiar with Shawshank Prison, from The Shawshank Redemption (1994). Teddy Duchamp was actually first mentioned in King's first book, Carrie (1976), in which Carrie destroys a gas station he once worked at.
The movie is based on a short story called "The Body" by Stephen King from a book of short stories called "Different Seasons" which also includes "Rita Hayworth and Shawshank Redemption" which became The Shawshank Redemption (1994) and "Apt Pupil" (Apt Pupil (1998)).
In the scene where Gordie and Chris race each other through the junkyard, Wil Wheaton could run faster than River Phoenix but Wheaton's character was supposed to lose. Wheaton had to fake a fast run when running slow so that Phoenix's character would win.
In the original theatrical release, the final words typed by The Writer, "Jesus, does anyone?" were obviously added in post-production. The size and color of the letters did not match the other words on the computer screen. This was re-shot for subsequent home video releases.
In the shot where Gordie and Vern are running towards the camera with the train right behind them, the train was actually at the far end of the trestle with the two actors on the opposite end. The crew used a 600mm long-focus lens that when shot at the telephoto end, it compressed the image so much it made it look like the train was right behind them.
Rob Reiner had trouble casting the role of "The Writer", first casting actor David Dukes, then going to Spinal Tap vet 'Michael McKean' among others, before finally settling on high school friend Richard Dreyfuss.
While filming the scene in which Ace Merrill takes Gordie's brother's Yankees cap, Kiefer Sutherland's first instinct was to put it on, rather than hand it to Eyeball Chambers. Reiner told Sutherland not to put the hat on as a way of showing that Ace was stealing it just to be cruel to Gordie and not because the hat itself was at all important to Ace. Sutherland and Wheaton both confirm in the DVD's behind the scenes documentary that the reason that Gordie never gets the hat back from Ace is that Ace threw it away immediately after stealing it from Gordie.
The apparel of the four boys is the same throughout the entire movie, except for Teddy. From the beginning to the tree house scene, he is wearing a nice shirt with a design on it. Then, he is seen wearing a green shirt, from the part where they all meet up to go on the journey, to the end of the movie. But Gordie, Chris, and Vern are all wearing the same clothes throughout the whole movie.
Rob Reiner developed a good working relationship with Stephen King after this movie, so much so that King only agreed to sell the film rights to Misery (1990) if Reiner directed the film. Reiner's production company, Castle Rock Entertainment, also went on to produce several other adaptations of King's stories. In addition, John Cusack went on to appear in the film 1408 (2007), and Kiefer Sutherland's father Donald Sutherland appeared in "Salem's Lot (2004)(TV)'.
An honest mistake was what helped Jerry O'Connell get the role of Vern. At auditions he got Rob Reiner mixed up with someone else. Rob Reiner stated in an interview, "He was exactly what we were looking for. At that moment I knew I was looking at what would be Vern Tessio."
Teddy says that he and his dad had fished the Royal River for "cossies." There is not a fish by that name, instead this is a joke and play on words. Cossies are 1950s-era one-piece bathing suits. The name derives from "costume" - the British call bathing suits "bathing costumes."
In the opening of the scene where Chris meets Gordie and shows him the gun, River Phoenix jumps from the back of a truck and says, "Thanks a lot" to the couple in the front: The truck was driven by Phoenix's friend, with Phoenix's mother riding in the passenger seat.
All four of the films stars have starred in music videos. Wil Wheaton and River Phoenix, appeared in Ben E. King's "Stand By Me" (made for the movie), Corey Feldman appeared in the video for Cyndi Lauper's "Goonies 'R' Good Enough" (made for the movie The Goonies) and Jerry O'Connell appeared in Mariah Carey's music video for her song "Heartbreaker".
The very next year, Wil Wheaton appeared on 'Star Trek: The Next Generation' as Ensign Wesley Crusher. His character, a young Starfleet officer serving as a Helmsman, was arguably analogous to the character Chekov from the original series. Wheaton would later lend his voice to various Romulan characters on Star Trek (2009), which featured Anton Yelchin as Chekov. Yelchin also began his career as a child in a Stephen King adaptation: Hearts in Atlantis (2001).
The trivia items below may give away important plot points.
When they were filming the scene where Gordie and Vern are about to be run over by the train, Wil Wheaton and Jerry O'Connell did not look scared enough; In frustration Rob Reiner yelled at them to the point where they started crying and that's when they were able to film the scene.
At the end of the film it is said that Chris (played by River Pheonix) dies trying to stop a fight, while the others went on with their lives. River Pheonix actually did end up dying from an overdose in 1993, while the other actors are still pursuing their careers.
After Rob Reiner screened the movie for Stephen King, Reiner noticed that King was visibly shaking and wasn't speaking. King left the room and upon his return, he told Reiner that the movie was the best adaptation of his work he had ever seen.