I think it contains some extra compared to just Kickstarter stuff. First of all the bonuses you get from Kickstarter depended on your pledge amount, so if you didn't pledge $50 or more, you didn't get all the goodies (sound track, concept art etc.). Second it contains the bonus item you get by registering Divinity Anthology.
It doesn't contain any additional missions or stuff like that. Just two in-game items that afaik are just funny, not useful.
