I think it depends very much on what you need to stockpile for. If, say, it's for emergencies, I reckon you would need less than would if you lived in a hurricane zone where it would, in the event of a disaster like Katrina, and even then, when THAT hurricane struck, people were evacuated from the area. In that case, you would be dependent on Government hand-outs, charitable donations and so forth. When WWII struck Europe, Britain had rationing, and provided recipe leaflets to help make supplies go further, and female work forces were sent off to till the land and produce much needed food. War zones are the worst, along with famines. We all know what famine does, and fortunately there are international organisations who send supplies to famine-struck areas, and help the local people with projects to cultivate crops, dig wells, irrigate and help people that way.
To a very much lesser extent, most of us stockpile for personal emergencies, and in that case it's simply a matter of calculating in the event of whatever happens. Personally, as we live in the countryside, it makes sense to have some reserves, although there are towns not far away. I'm a hoarder anyway, and we always have plenty of stuff. But I always give something by way of food to the Libyan refugees on the streets. I'm by no means a Saint Di, but I feel sorry for these guys.
Enough is never as good as a feast Oscar Wilde