what i am reading at the moment

A couple of weeks ago i started reading Harry Potter again from beginning to end and i am half way through the sixth book. While reading through them I have realised that the films have missed quite a bit from the book, important stuff like the coins they use for DA lessons to let each other know what time and day the next ones going to be at. I only mention this point because the coins are used later on when a big fight breaks out in school which as totally been missed out by the film. i thought personally that this point would have been important because it shows the school standing together and fighting together. but obviously this means different things to everyone what do you think?