Jewish memorial candles (Yahrtzeit Candles) are burned by jews observing the anniversary of the death of a loved one. However, they are also useful in emergencies.

They burn for at least 24 hours and come in convenient glass cups. They are small and made of parafin. You can find them in the "jewish" or "ethnic" section of any major supermarket for about two bucks.

This is no substitute for a good flashlight, but for general at-home illumination in a blackout, it's a useful thing to have.