I'm curious, could you use the bottom of a jar as a solar concentrator for starting a fire? Could be lens shaped enough. If not, I think you can use a glass jar full of water to do it. As long as you sealed the jar to keep from losing any water, I think that's as much worth a try as the soda can and chocolate. Anyone else spot ways to start a fire he might have used?
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A gentleman should always be able to break his fast in the manner of a gentleman where so ever he may find himself.--Good Omens