They could make it so you can only carry a certain amount of food with you. So, say, you could head into the dungeon with three days worth of food and there might be some more food available in the dungeon. You shouldn't need more than that to make it through, but if things go poorly, you can always leave the dungeon to restock - there doesn't need to be scarcity in the world if you're limited in what you can keep with you at any given moment.