Coffee can + paint can + toilet paper + aclohol == portable heater. I would be a little leery of using this an a heater in a car like one suggestion for an emergancy (would think you might set the car on fire. But for a campsite, this might be good.
http://preparednotscared.blogspot.com/2010/01/preparedness-project-paint-can-heaters.html?m=1