One change from the book that I loved...
The smoking! (tobacco)
In the book, Charlie smoked cigarettes a lot. It was mentioned several times throughout the book. First of all, I hate that cliche of making a character smoke to give them depth. Like, seriously, it is one of the stupidest tropes ever and I'm glad they took that away for the film. I believe that if I read the book first, I would have thought Charlie was a mere expy of Holden Caulfield (they already share many other traits).