TLDR: What stories are part of The Hobbit film(s) other than The Hobbit? Thanks!
Addition of Legolas and Tauriel into the Hobbit. Legolas was taken straight from the Lord of the Rings and Jackson introduced Tauriel himself. People say this helps to greatly increase the audience's engagement with the Elves of Mirkwood.
The character of Radagast has been expanded in the film. In the book, the scene where Radagast helps the dwarves in escaping the Orc Warg riders doesn't exist, it's purely in the film.
In the book, Azog the defiler was beheaded by Thorin's cousin before the events of the book, where as he plays an important role in the film.
In the film, Galadriel explains how the Witch King was killed and sealed in a tomb in the high fells. This is different in the book, where it is explained that the Witch King simply fled from the battle, still alive. This is linked to the prophecy in the Lord of the Rings, where it is stated he can not be killed by man, which results in Eowyn killing him in the LotR films. This prophecy doesn't make sense if we follow the events of the The Hobbit film.
In the book, the goblin tunnels were made solely of just tunnels, there were no rope bridges.
Also in the film there is a brief cameo appearance by Frodo Baggins, which doesn't happen in the book.
But you need to consider the fact that the Hobbit book itself was re-visited and edited by Tolkien, to fit in more with the Lord of the Rings (as it was written before.)
The first Hobbit was written in 1937. In the first edition, Gollum was willing to bet his ring in the game of riddles with Bilbo. Finding that he's lost it after Bilbo has won makes Gollum courteously show Bilbo out of the caverns.
Before the edits to the book, the ring was seen as a 'Convenient Magical Device', however after the Lord of the Rings this changed to an irresistible power object.
I hope this helps