Pony's hair is supposed to be like Soda's hair but slightly redder. Steve's hair is supposed to be slicked back in very complicated black swirls. Two-Bit's supposed to be tall with rusty hair and exaggerated sideburns. The movie cut out all of the Sandy drama I thought the movie made Two-Bit more serious. He cracked some jokes, but the book made him out to be fiercely playful and whatnot, almost always being wise. The movie placed a bit of emphasis -- not much, but still -- on Dally's necklace, which was nonexistent in the book. In the movie, he wore a St.
Christopher medallion. The movie made Soda seem considerably less happy than the book made him out to be -- that is, the book made it clear he was naturally a happy person who got "drunk off life," but in the movie, he was awfully happy a lot of the time so the audience didn't know this character trait. The movie skims over Pony's illness after the rumble, during which time Randy visits their home. The regular movie edition skips the entire first chapter pretty solidly, but the extended opening does tell you about the first chapter.
The movie makes no mention of Soda's horse, Mickey Mouse. It also ignores Soda's past dabbling in rodeo bronco-riding. In the movie, the Socs are from the south side of town and the greasers are from the north. In the book, the Socs are from the west and the greasers from the east. In the movie, when Pony comes home from the lot at two in the morning, Darry shoves him hard and he falls. In the book Darry just slaps him across the face.
The movie, understandably, drops some of the banter between Two-Bit and Marcia at the movies. As far as I remember the movie didn't include Dally messing around. Little scenes like Dally terrorizing those kids weren't in the book. The movie showed Dally alone at the store when he held it up, whereas the book didn't describe that. The movie showed Pony's dreams. The movie never mentions that girl who looks good in yellow, the one who called Pony a hood when he whipped out his blade during class to cut a worm.