With The Book Thief, adapting it into a movie makes the most sense since it is a long, drawn out story. A musical wouldn't make much sense to me because there are no songs and it is not a particularly happy story. A TV series doesn't quite fit the writing because the events in the book don't really happen individually. It's more of everything happening all at once.
Some events and side stories in the book could be cut without altering the story. These events would be the back story of Rudy painting himself black and imagining that he was Jesse Owens, and when Liesel and Rudy go with the other boys to steal apples and potatoes. I really don't feel that those events contributed anything to the actual story. Even though those events should be cut, the character of Rudy shouldn't because he plays a very vital role in Liesel's life.
The most unique thing about The Book Thief is that the whole story is told from the point of view of Death. It really personifies death and gives him a "grim reaper" image. It is interesting how this character of Death becomes so fascinated in this little girl who steals books. When doing a movie about The Book Thief, it should be narrated by Death, like it is in the book.