It's difficult for us to imagine, but people actually got along without electric power for thousands of years. Some people still get along without it today. But in 21st-century America, not being able to switch on the lights or heat the house with the furnace are things we just aren't prepared for — literally.

Even so, power outages do happen (you can track them here), and sometimes they last a while. So preparing for a power failure is a wise investment, even if of a different sort than we usually discuss here.

Fortunately, most outages aren't as severe as the pair of week-long outages endured by Sound Mind Investing's home city of Louisville, Ky., during the past year. But if you're not prepared, even a short power outage can create serious challenges. And if the weather is really bad (such as during Louisville's winter ice storm in January), the implications can quickly escalate.

To be sure, the definition of "prepared" will vary depending on where you live and the events surrounding the outage. Being snowed in without power is quite different than having a spring thunderstorm knock the power out for an evening down south. But no matter the time or place, the general areas of preparation remain the same.

Here's a rundown of the top preparation categories, plus ballpark figures of what a "readiness investment" is likely to cost.

• Light. There's no substitute for investing in a few well-built flashlights and fresh batteries (hand-crank LED lights are also fantastic for such occasions).

A battery-operated lantern that offers general rather than focused illumination is also well worth it. (Experts say it's better not to use candles and oil lamps because of the fire hazard.)

Cost of "light" preparation: $50-$100.

• Communications. Cordless telephones don't work when the power fails, and cell phones will run out of juice within a few hours. So be sure you have at least one corded phone in your house. (Of course, it won't work either if the lines are down).

For your cell phone(s), buy a charging adapter that plugs into the lighter in your car. Also, get a battery-operated or hand-cranked radio to keep you abreast of news and weather information.

Cost of "communications" preparation: $75-$150.

• Heat. If you live in a cold climate, you'll need to figure out a method for keeping at least one room warm. If you already have gas logs, a wood-burning stove, or a fireplace, you should be in good shape (although without an electric blower, a fireplace isn't a very efficient heat source). If you don't have an alternate source of heat, a propane or kerosene heater may be a good option.

Another option worthy of strong consideration is a portable generator. A generator will allow you to run an electric heater, as well as other small appliances and items like a laptop computer (so you can work while waiting for the power to be restored).