A restaurant could sell 10 meals worth for 10 * original_price * 0.5 and make more per order plus use up more ingredients. Farms could sell cheese by 5lb packs, eggs by the dozen dozens, meat by 10lb packs, etc.
It's not worth the whole ordeal of going to a restaurant to get a small portion of food, pay the same price as a sit-down experience, and be hungry again in a few hours.