As for the food in the cafeteria, it is buffet-style, and you can find food from all sorts of places (this is an international school after all). There is also a counter where your character can go order a specific kind of food. You can all imagine that when answering the "One word that you need to survive" question, a lot of people have answered with 'food' or 'water'. So yes, the people operating at the counter are alumni of the school and can make any food appear.