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.
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.
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.
In the swamp, the four boys get completely wet, then they strip down to their underwear to remove all the leeches, and Gordie faints after a leech is found on his nuts. The next scene when the boys are putting their clothes back on, they and their clothes and sleeping bags are completely dry.