You rotate stock and only stock things you use. When something goes on a good sale, buy it and put it in the back of the stack. Keep an eye on expiration dates so you don't forget to use something in time (bearing in mind that canned goods are still safe after the expiration date for quite awhile.) Don't buy something and stick it in the basement, throw it out every other year and replace. That's just stupid and wasteful. Keep all your foods together, stacked neatly and organized in a logical fashion, and just keep a larger quantity of it around (non-perishables.) You just need to get organized and keep everything in a convenient location (as near to the kitchen as possible if not in the kitchen itself.)
I don't stockpile food for emergencies, but I live way out in the country and can't just run to the store for one thing, so I try to keep my pantry and freezers full enough that I don't have to go shopping every other day (I hate shopping and I do all of the shopping for my family myself). I am usually conveniently prepared to weather any storm up to a couple week long, and perhaps even a couple months if needed.