DISASTER PREPAREDNESS UPDATE: Reader Jim Hogue emails: "Do you have any recommendations for flashlights in a survival kit?"
Well, personally I'm a big fan of the mag-lites. I carry both a mini and a full-size 4-cell in the car, and I keep a few of the big ones around the house. They're tough, they give great, adjustable light, and they make a pretty good improvised billy club just in case.
On the other hand, you have to keep the batteries up. As it happens, I was just looking at this zombie-attack preparation guide (what is it with the zombies all the time?) and it features this batteryless flashlight. That looks kind of cool; I don't think it's as good a flashlight as the maglites, but you don't need batteries, which also saves on weight. A lot depends on what you think you'll need it for, and for how long. Or you could always carry this survival tool -- pocket knife, magnesium firestarter, and flashlight all in one. BoingBoing liked it! And if you want versatility, here's a flashlight that uses AA, C, or D batteries, which is pretty versatile. I bought one a while back -- it's not bad, but doesn't seem especially sturdy.
I have to say that my cheap Timex Ironman watch makes a good emergency flashlight, too. It's not terribly bright, but it's enough to find your way around in the dark without bumping into things. I was in the grocery store -- in the meat section, about a half-mile from the windows at the front -- when the power went out a while back. The place was pitch-dark and it took about 20-30 seconds for the emergency lights to come on. As soon as things went black a woman started screaming -- I guess she had claustrophobia issues -- and I pushed the light button on my watch. This calmed her immediately, strangely enough. Then a few people opened up cellphones and it was a brief impromptu light show.
The watch is nice, though, because you've always got it. (As with cameras, guns, and many other things, the one you've got with you is always more important than the one you've left in a drawer at home). It's actually stopped me from buying a more expensive watch, as you can't get the "indiglo" feature on the fancy watches.