I've accumulated enough stockpiled food that I basically follow dcompton's goal - I shop at home for meal planning. Rarely is an item on my grocery list anything other than what is needed to replace things in storage AND it's nearly always on sale. Most of my purchases are based on loss leaders/discounted items/manager's specials.
When I have a jar of peanut butter in storage that has a fairly close use-by date, that's when I add peanut butter cookies to the meal plans, or other recipes that include peanut butter - choose peanut butter toast for breakfast a couple times a week, etc. Otherwise, we normally use one 16-oz. jar of peanut butter per week. Knowing that, I can see how many I can realistically keep in storage by the use-by dates of them.
I may be down to my last 1-3 of something-er-other, but I'll wait for a STRIKE POINT to purchase it (the point at which you know it's the lowest price - because I keep a PRICE BOOK -
http://www.getrichslowly.org/blog/2007/05/02/use-a-grocery-price-book-to-slash-your-food-spending/ - and log prices in it for reference) . I'll also be on the look-out for coupons and rebates for those items so I can stack savings. (On sale, with a coupon, on double/triple coupon day, PLUS a rebate = optimal savings.) I don't have very many cans of pork n' beans just now because I'm waiting for the summertime sales that generally occur just before a big cook-out holiday several times during the summer.
As others said, most of us started by buying an extra one or two of something when it was on sale. Eventually the cabinets get full and you have to use more organized storage. Shelve items by use-by dates and use the closest dates first, and keep an inventory.
I always suggest getting a variety of foods that cover all the food groups and store ingredients with which to make a large variety of foods, instead of large numbers of pre-made convenience foods. "Ingredients" are usually less expensive than convenience foods and highly-processed foods.
If anyone is thinking "survival" mode (layoff, power outages, natural or man-made disasters, $ need to go to something other than food, interrupted food supplies, etc.) you may want to stock what are often termed the "Seven Survival Foods" first:
-grains
-legumes
-sprouting seeds
-honey (or sweetener or choice)
-salt
-oil
-powdered milk
I keep several years worth of these items and everything else is 6-12-months. It took several years to accomplish this because I did it within my grocery budget, not extra money set aside for stockpiling. I always used a portion of my food budget FOR stockpiling - at least $5 a week purchased food destined for the shelves in storage.
Even if you don't have a mill, you can make all kinds of things from whole wheat berries. Small amounts of a coarse flour can be milled in spice/coffee mill. I use a Sue Gregg recipe and make
Blender Batter Waffles/ Pancakes from whole grain.
www.suegregg.com (click on the picture of the batter being poured on the waffle iron for the recipe). If you don't have any fresh veggies, sprout wheat and you'll have the nutrition of fresh vegetables.
Carrot & Pineapple Salad
1-1/2 c. shredded carrots
1 small, 8-oz. can crushed pineapple, drained
2 c. cooked whole kernel wheat
1/2 c. salad oil
Combine all ingredients. Chill. For variety, you may add nuts, bananas, apple pieces and raisins.
Grainlady note: You can "cook" wheat in a Thermos: 1 c. whole wheat berries, 2 c. boiling water, 1/2 t. salt. Place hot tape water in a quart-size Thermos to pre-heat it. Dump out the hot water and add the wheat and salt and the boiling water. Close the Thermos and set it on it's side to better distribute the water and the wheat. Leave overnight. Cooked wheat can also be used as a breakfast cereal. You can also "cook" rice and beans in a Thermos.