All of them look right to me. "One more" and "another" would be used when the food comes in countable 'chunks'. ex. chips, apples etc. "Some more" would be used when the food isn't.

By default, C is correct. We don't know if it's soup, spaghetti, a slice of pizza, etc. In the question "Have you and enough to eat?" it is implied "Have you had enough food to eat?" And the only correct answer to "food", which is uncountable as a word, is C.