If you just want to have a flashlight on you in case of power failure, get a cheap coin cell light and put it on your keys. They're not ultra bright, but they are plenty to light your way out of a building, and will run for a very long time. I just tested one and even after 24 hours nonstop it was still bright enough to get around indoors when dark adapted, and it's fairly reasonable up til about 8 hours. Or if you want to support ETS, get Doug's version of the Photon Freedom, which has dimming and signalling modes, and will run a ridiculous amount of time at the dimmest setting.