Interesting. Had no idea the releases varied so much. I generally don't delve too deep into the extras, but surprised so much gets taken out. I also found this, which details all the global releases if it's of interest... http://www.dvdcompare.net/comparisons/film.php?fid=34643
A fair amount of content (info taken from blu-ray.com review); Story of the Story (1080p, 10:30): Voice cast and crew look at story origins and development, character and world design and evolution, story arcs, and themes. Mapping the Mind (1080p, 8:24): A closer look at designing and implementing the film's expansive main setting, the mind of an 11-year-old girl. Our Dads, the Filmmakers (1080p, 7:25): Elie Docter and Gracie Giacchino document their fathers' work on the film. Into the Unknown: The Sound of Inside Out (1080p, 7:09): A brief exploration of the sound effects used in the film and the process of finding them, fine-tuning them to the world, ensuring they elicit the intended audience reaction, and recording them. The Misunderstood Art of Animation Film Editing (1080p, 4:43): As the title suggests, this piece looks at the editing process, which is more complicated than simply adding scenes together. Mind Candy (1080p, 14:26): A compilation of extra character moments. Deleted Scenes (1080p): A Pete Docter General Introduction (0:55) is followed by several deleted scenes, including Riley Grows Up (4:45), Joy's Decline (3:42), Misdirection (4:12), and Construction (3:17). Docter also briefly introduces each scene. Note that scenes are presented in the form of early storyboard renditions and are not complete. Trailers (1080p): Remember (1:38), Experience (2:19), and Japan Trailer (2:30
Out of interest, what's on the US Bonus disc that isn't on the special features on the UK version?
Unfortunately both the standard & 3D UK releases are missing the bonus disc. So if you are after that, you'll either have to track down the original US releases (Disney US are at it now too, new 2018 release is only 1 disc), the Australian 2 disc release or one of the Nordic 2 disc releases. EDIT: The UK did have a 3 disc Zavvi steelbook, 2D + 3D + Bonus, but that was £25 and long OOP (minimum £22 used at CEX).