A book of matches fits perfectly inside the top of the mason jar survival candles we posted about a while back. Makes sure that you have a light on hand for getting the candle going.
I've put one of these in each vehicle and have a box stored for use at home. We've also made some scented ones that see fairly regular use...it's been almost 2 months and they still have about 1/2 of the wax left in them.
Fun project--give it a shot if you haven't yet! Here's the original instructions.