Just want to point out that being prepared can actually be less expensive than not, not to mention more healthy and more tasty. We buy rice & grains in bulk because it's cheaper that way. Buying big cuts of meat on sale(especially after the holidays) and then pressure canning them is not only cheaper, it provides a delicious quick meal. A pint of canned lamb shoulder and a pot of rice is really a good meal .... add some home canned or store-bought peas and it's pretty well balanced. You may not know what goes into the meat before you get it, but if you home can it at least you know what goes in after.
We can as many of the fresh veggies as possible from our small garden (we re-discovered home canned 'maters a few years ago and store-bought can't compare).
Home canned foods can be eaten straight from the jar, requiring no fuel at all.
A small home drier can also provide easily stored food that is really good to eat. Try some dried tomatoes, they take much less room than even home canned 'maters and come back well with minimal fuel usage. You can also dry onions, squash, most fruit(even watermelon), greens & cabbage(which dry to almost nothing and "cook" in just a couple minutes), peppers & mushrooms can be simply dried on a string hanging in the kitchen. Dried food takes less room to store and is "edible" for a long time.
There are a lot of edibles growing in and around your yard if you know what to look for. Having a few field guides on the shelf is smart. Even if you never have a reason to try dandelion soup or steamed nettle, knowing what & where they are could come in handy.
Fuel to cook with is something to think about. The Haitians stripped most of their side of the island of trees in just a few months after the quake. If you have to cook or boil water you need to have plenty of dry fuel on hand. If you don't or haven't heated with wood you'd be surprised how much you can go thru in a month. Most of us would be hard put to keep warm with nothing but an axe to cut wood with.
Bottom line for me, I'm not considering a nuke attack, natural disasters are more likely to put us in a bad spot. An economic crisis is also more likely to cause long term hardships than a hostile attack. I've enough put away to get us thru a few weeks if we're careful. Not because I'm necessarily planning for a disaster, but mainly because it's cheaper and healthier.
Beyond a month or 2 is a whole 'nother ballgame. I don't believe that many folks could make it more than 2-3 months no matter how well prepared they think they are. I'm not knocking those folks that stockpile thousands of rounds of ammo, it's their $$. I just don't think you can keep people from getting your supplies if they know you have them. You have to remember that in the apocalyptic situation there will be remnants of the military roaming about. Sorry boys but an AK with 1000 or 100000 rounds won't help much against a tank or mortar. The people that will make it the longest in that scenario are the most predatory. I don't personally think I have what it takes to steal from other families (or even refuse to share) if it means that they won't have what they need to survive. Guess I'm just too civilized.