How to prepare the light
I used Holiday Time Tea Lights but you can really get away with any tea lights you want, or even just buy a batch of flickering LEDs from Evil Mad Scientist (I know for a fact flickering red and flickering yellow together look amazing).
If you use just raw LEDs, tape the leads (yes, seriously, tape) to either side of a CR 2032 battery, and it should last for like a week.
If you want to use the tea lights, you get the advantage that they have an on and off switch. The pictures below tell how to prepare a holiday time tea light for the oven.