One of the books that Liesel read to Max when he was sick is actually the book The Book Thief itself, containing the sentence: "what came to her then was the dustiness of the floor, the feeling that her clothes were more next to her than on her, and the sudden realisation that this would all be for nothing".
When first arriving at the school, a large poster with many faces can be seen. This is a replica of an accurate period piece, a poster depicting the "ideal" Aryan phenotypes according to the region. Painted by two artists with racial obsession, these posters were placed in every school, and students are forced to memorize them.
When Nelisse was told she was acting with Emily Watson, she thought they meant Emma Watson from the Harry Potter franchise. She told everyone she would act next to Hermoine until her mother eventually told her that wasn't the case.
Emily Watson decided to stay in character all day, which meant that in between takes she was still acting as a grumpy German woman. It caused her to get into a fight at the airport when she reacted like her character would do at check-in which caused her some problems.
Liesel's book theft is explored more in the book, and the Mayor's wife even tries to catch her doing it; a deleted scene does have Liesel and Rudy stealing a book with her watching them.