I was surprised to learn the other day that giving food donations to the food bank is the least efficient form of helping them out. Because you are paying retail prices for the food you give, you are overpaying quite a bit. If you were just to give them a small amount of money, such as ten dollars, they would be able to purchase far more food with that cash than you are, because of their connections to various bulk and discount food suppliers.
You can read more about this here.