Taking into account the Lord of the Rings Appendices and all of Tolkien's other writings (including his letters) I'd like to know what elements of the film were entirely created by Peter Jackson and Company.
If this question is too broad as asked, please let me know how I might improve it!
(I hope this question isn't going to be confused with What elements from non-Hobbit Tolkien canon have been included in the Hobbit movie?)
I'll take a stab at this since I was so disappointed that they didn't try to follow the proper story more.
Thorin wasn't late, he arrived with the group of dwarves who fell in the door when Bilbo opened it and that was the same time that Gandalf arrived.
The dwarves brought a lot more instruments to play (I always thought that was a little silly and wondered where they all went the next day when the dwarves set off. I can't imagine they brought drums and violins on the journey).
The morning after the party Gandalf comes around to hurry Bilbo out the door and that is the first time he gets anything in writing about the contract. It was actually left on his mantle but he didn't notice it.
Gandalf doesn't leave the dwarves on the road out of anger. No one actually noticed he was gone until they needed him.
The trolls don't steal the ponies. The company is having a miserable night because of the rain and can't light a fire but when they spot a fire off in the distance they send Bilbo to investigate.
Bilbo tries to steal a purse from one of the trolls in order to prove his burglar skills but it yells and gets him caught.
The other dwarves get caught without any real fight when they come looking for Bilbo except Thorin who does put up a fight but is overwhelmed.
It is Gandalf, not Bilbo, who confuses the trolls by throwing his voice until the dawn.
There is none of this pale orc nonsense in the book and the wolves don't come until they reach the other side of the Misty Mountains.
Radagast and the stupid rabbit sled thing -- 'nuff said.
There should not be any of this animosity between Elrond's people and the dwarves. In fact, the elves of Rivendell are expecting the company and singing songs about them when they arrive.
There was no council with Saruman and Galadriel. All the stuff about Dol Guldur is happening but is outside the scope of the book. (I kinda don't mind them adding stuff like this since it did, at least, happen in the original story)
The dwarves did not leave Rivendell without Gandalf.
They did not walk around on the giants knees -- that part of the movie was just stupid IMHO, all we needed next was Optimus Prime to show up and save the day.
Gandalf was in the cave with the dwarves when the goblins captured them. He killed several and then just managed to sneak inside before they closed the door.
Bilbo was taken before the Great Goblin with the rest of the dwarves. He was rescued by Gandalf, same as everyone else and Gandalf killed the Great Goblin and then he and the company fled.
They were in tunnels, not big open spaces with lots of rope and wood bridges.
Bilbo was lost in the flight after the Great Goblin was killed. That was when he found the ring while fumbling around in the dark.
The riddle match happened while the dwarves and Gandalf escaped. Bilbo was noticeably later getting out.
There was no mention of Bilbo having blurred sepia vision while wearing the ring. (I know, this was more creative liberty carried over from LOTR)
Bilbo lost his buttons getting out of goblin's gate to the outside, not getting away from Gollum. This was kinda important because A) it was still daylight which is why the goblins hadn't given chase yet and B) the goblins spotted Bilbo's shadow.
It was the wolves (not wargs) and goblins (not that stupid pale orc) that treed the dwarves and Gandalf. They did not push the trees over the edge of a cliff.
There was no climatic rescue of Thorin by Bilbo.
They could not see Erebor from the slopes of the Misty Mountains.
This is all I can think of off the top of my head after only seeing the movie once. There are probably a lot more since it seems they didn't even try to stick to the original story. I can't wait to see how badly they mangle everything in the next two movies.
The addition that most strongly contradicts Tolkien's timeline was to have Radagast discover the Necromancer at Dol Guldur. It will allow the movies to have one coherent story but grates really badly against canon.
You see, in the canon timeline the Necromancer had first appeared at Dol Guldur almost 2000 years before the events of The Hobbit, and Gandalf had gone there (and confirmed that it was Sauron) almost 100 years before, which was also the time when he acquired the map and key from Thorin's dying father.
This is vitally important because it explains why Gandalf personally accompanied and helped Thorin on his quest: it was really a carefully planned diversion to prevent Smaug from helping Sauron when the White Council attacked Dol Guldur.
Excellent answer which sums up most of my disappointments with the film.
I'll just add that the coming of Smaug is different in the film. All those homeless dwarves roaming the plain would have been a nice feast. In fact the dwarves inside were all killed except for Thror and Thrain who mysteriously appeared on the mountain-side somewhat singed (setting up the later revelation of the secret passage). The Wood-Elves weren't there and didn't refuse to help. Also Thorin seemed to already have the map but not the key, and Balin would never question Thorin's actions in the presence of others.
Gandalf didn't use a moth to seek help (similar invention in LotR) but the Lord of the Eagles just happened to notice the commotion. Bilbo didn't make any heroic gestures of saving Thorin, or anyone else, during the goblin attack while they were in the trees.
Another non canon element where that Thorin actually were outside the castle when it was under attack. That was the only reason he survived. His dad and granddad took the secret exit. It wasn't as manny people that survived in the book. Most of them got killed.
