diversity in your meal choices. You buy bread, you can make some version of meat and cheese sandwiches, but the meat and cheese come in probably 3-4 serving quantities. A can of tuna makes a couple sandwiches. The point is that people WASTE almost as much as they consume unless they are producing for a family.

And then there is the overpurchasing that happens when you hit the store. Doesn't really happen in a restaurant as much.