I assume they included this as a sentence because the two words sound similar.
Can someone explain why it's not just "Könyv vagy kenyér"? There is no other subject in the sentence right?
When the subject and verb are omitted, the remaining object is in the accusative. (book or bread is not a subject, so it's not in nominative case)
It's the same in English, except there is no difference between nominative and accusative most of the time. We would never say He or she?, but rather, Him or Her?