In the past, my family would acquire a year and a half of food storage and then we would not think about it for a while. Every time I needed to see how much food we had, it was like I had to start over on figuring out how much we had and what we needed, and if we had enough for my growing family.
I finally made a chart where I tallied up what we had, and filled in the gaps with what we needed by hitting case lot sales. Then I placed a chart on the door to our food storage room which was marked every time we used something from that room. If we used a can of black beans, we would make a hash mark by that item on the list. Now I take the list with me to the store every six months and stock up on what we use the most of instead of randomly guessing what we might need.
Suggested amounts of basic foods for home storage (from an official letter from Church Headquarters):
Per adult for one year:
Grains: 400 lb
Legumes: 60 lbs (beans, split peas, lentils, etc.)
Powdered milk: 16 lbs
Cooking oil: 10 qts.
Sugar or honey: 60 lbs
Salt: 8 lbs
Water (2 weeks): 14 gallons
See also http://www.providentliving.com for suggestions