First, decide what kind of preparation level you want your household to be at. Pick a number of days, which is mostly personal preference. My magic number is 14; maybe yours is 30 or 60, or over 700. (Maybe your state National Guard will order you to evacuate after a certain number of weeks anyway.) Or maybe your number is zero -- in which case you want cash and your important documents, on paper or scanned into a flash drive, in a ziploc bag ready to go. Consider including a map in the bag, and some important phone numbers and addresses, so you're not dependent on your phone or mobile device after the battery goes and there's no way to re-charge it.
Second, figure out how much food, water, and toiletries you need per day. There are so many guides and websites available to help with this aspect of emergency preparedness that I hesitate to link to anything. The U.S. National Hurricane Center offers a printer-friendly checklist; FEMA's instructions include suggestions for storage and maintenance. Googling "disaster supply kit" will yield all kinds of solutions, from free information to pre-packed "deluxe" backpacks.
You can always compile your own kit for less money, and with a more complete kit, than what you'll pay for a pre-packed kit.
Third, decide what you'll stock up on: extra prescription medicines, toiletries, water, and food for [insert chosen time period here]; plus a flashlight or two, a radio, and batteries to power them if they're not shake- or crank-powered. (Most of the lists emphasize first aid kits, but don't you have one already? Make it your household storage rule to replenish the band-aids, bactine, and antihistamines all the time, and you're set.) If you are uptight like me, the current supply of toiletries that you have on hand right now would already last you for several days, if not weeks or even months. Bar soap, for instance, is cheapest when I buy it in large packs that happen to last for six months in my household; and a single tube of toothpaste lasts longer than my "chosen time period" of two weeks. But I don't have my spare toiletries packed together in a kit; I keep them where they belong, in my bathroom drawers and linen closet -- because why bother? Why pack all this stuff into a bin that I have to dig through just because the power went out?
Storing an earthquake kit and stocking a storm cellar are different. But my emergency preparedness scenario -- regular, if infrequent, utilities and services outages, and the exceedingly low risk of a situation where I need to abandon my home -- don't contemplate severe or complete destruction of my dwelling.
As for food, you can spend a lot of money or you can spend only a little. You can stock up two weeks' worth of nutritious food for just a few dollars; you'll simply have to tolerate eating very simple food. We're not talking elegant meals here. We're talking filling your stomach cheaply. To spend a lot of money, buy military MREs. You can find them online for about $80 per dozen, and two of them will give you enough calories and nutrients for a sedentary day in clement weather. To spend only a little money, stock up on canned food (for carbohydrates and protein) and dried fruit (for vitamins and fiber). Ask at your supermarket if you can get a bulk discount for buying a case of pork and beans or canned pasta. Get some dried beans for sprouting if you like, for extra Vitamin C. I keep on hand some instant lunch products, the type of factory-made near-food in a one-use, disposable container that I don't otherwise eat, for variety, but I buy them only when they're on sale.
Dig your budget. Prioritize building up your pantry, saving up for a crank radio, and finding cheap candles (N.B., holiday candles are really cheap the day after the holiday). Add a single emergency preparedness item to your grocery list every week. Then can by can, package by package, and bottle by bottle, you'll eventually have an emergency supply of food. And when the emergency comes -- remembering that we get a good week's notice of incoming hurricanes here -- you won't have to run around the city looking for batteries.
What did I leave out? Is my privilege showing? Why isn't basic emergency preparedness realistic for some people, and are you one of those people? Please comment. Thanks!