Simply keeping a two week food diary can make food storage planning a lot easier. Most people do not have a real idea of how much food they consume over a period of time. From your food diary you can extrapolate your food usages for almost any period of time. To find one week divide by two. To find four weeks, multiple by two.
This gives you a basis for determining your long term needs. You now know what your family actually eats. We are in the process of doing this and will report on how it has affected our long term goals.