Imagine a lockerwall for your groceries. In the morning you can bring your leftover products. Input what you brought and a locket will be assigned (cooled if needed). During the day you can see what is being added an you can shop / reserve an item (bring one, get one). At the end of the day you go home and pick up the one thing you needed. And if not all products have been taken at the and of the day. The food can be used by the salvation army (or simular).