Yep, what he said. It’s a six-month supply now that’s recommended for most people, since few have the space for a whole year.
Food storage serves a whole bunch of purposes, the apocalypse being one of the less prominent ones. 72-hour kits are just for emergencies in general–if there’s a wildfire, an earthquake, a flood, or what-have-you, you can take your kit with you and not have to worry about what you’re going to eat, drink, or wear in the immediate future–thus lessening the burden on whatever relief is available (if any) and being in a better position to help others.
A large, long-term pantry is practical for lots of things–huge storms that make it difficult to leave the house, long power outages, employment woes, spikes in food prices, food panics, that sort of thing. When you lose your job, it’s nice to know that at least you won’t starve any time soon. It saves a lot of money to have food storage, since you can buy everything in bulk on sale and just have it on hand, skipping purchases when they’re not on sale. When a storm hits and everyone is buying all the bottled water, you don’t even have to go to the store. And you can share with your neighbors.
And, should things get really difficult someday, you’ve got a lot of wheat and rice and beans to eat. The LDS Church maintains its own store of such things as well, and is frequently the first to show up with emergency food relief, because it’s all ready to go. (If you’re ever in Salt Lake City, a tour of Welfare Square is truly fascinating, I recommend it.)
We’re also big on gardens, producing your own food, and self-sufficiency in general, as much as possible. Even if you live in an urban apartment, you can grow tomatoes on the balcony and keep extra food under the bed.
Of course, actual Mormons vary in how well they manage food storage. I need a lot of improvement! But I also have a friend whose husband is a real estate agent in an area that has tanked–she’s been feeding her family on food storage and fresh food from garden/friends for months now, nearly a year. Every once in a while she gets a little money and spends it on meat or something, but she almost never goes to the store and is living on almost no income at all.