1The Leaky Cauldron
In Harry Potter and the Philosopher’s Stone, the sign for “The Leaky Cauldron” is completely black, probably to keep it a secret from the Muggles, but the sign reveals itself when Harry and Hagrid approach it.
In Harry Potter and the Philosopher’s Stone, when Harry, Ron, and Hermoine enter the Wizard's Chess room, the remnants of Professor Quirrell’s chess match can be seen around the edge of the room, giving the audience another clue that someone had come this way recently. In the book, broken pieces aren’t mentioned, but the Flying Key’s broken wing is mentioned.
Despite many instances of Harry being noted as a “great wizard”, Harry does not, in fact, cast a single spell during the entire first movie.
In the first movie, Draco Malfoy says to Ron “Red hair and a hand-me-down robe? You must be a Weasley.” This detail is carried over visually to the second film very well. In Harry Potter and the Chamber of Secrets, Ron’s robes are older than everyone else’s, as they are hand-me-downs. The Weasleys win a sizeable amount of money in the lottery over the summer between second and the third movie and sure enough, his robes don't look too dingy in the third movie.
In Harry Potter and the Chamber of Secrets, a wig can be seen on the table of Professor Gilderoy Lockhart, probably suggesting that he is bald.
In Harry Potter and the Chamber of Secrets, “Sherbet Lemon” is the password used to enter Dumbledore’s office. Albus Dumbledore was particularly fond of these Muggle sweets and in Harry Potter and the Half-Blood Prince, there’s a bowl of them on his desk.
The opal necklace, which plays an important role in Harry Potter and the Half-Blood Prince, can briefly `be glimpsed in the second movie inside a display case in Borgin and Burkes’ shop in Knockturn Alley when Harry first enters it.
In Harry Potter and the Prisoner of Azkaban, Hermione can be seen tucking away her Time-Turner early on. Throughout the movie in fact, pretty much anytime someone comments on how she got there or when she isn't wearing her jumper or robe, the Time-Turner is visible around her neck.
9Weasley family in Egypt
Early in Harry Potter and the Prisoner of Azkaban, Harry sees a newspaper article with a photograph of the Weasley family in Egypt. Though it is never again mentioned in the movie, this is a very important plot point in the book. While on an inspection of Azkaban, the Minister of Magic had a copy of that paper, gave it to Sirius Black, who recognized that Peter Pettigrew was disguised as Scabbers. This is why he decided to break out of Azkaban, track down Scabbers at Hogwarts, and take his revenge by killing him.
In Harry Potter and the Goblet of Fire, in the scene with Dumbledore, Harry, and the Pensieve, there is a 3D model of what looks like Hallows Symbol which becomes an important symbol in Harry Potter and the Deathly Hallows. Though the final book was not yet written when this movie came out, J.K. Rowling had a lot of influence over the movie details and she added lots of objects and plots in the movies that were referenced later.