Since this type of verbiage seems to be pretty common, I have two comments in reply to:

"I've read that Sterno gives off enough heat to keep the temp above freezing in an auto.”

1. Any claim about attainable vehicle inside temperature is completely useless without reference to the allowable outside weather conditions under which this is possible. For example, it takes a lot more BTU production at -40 deg F than at +20 deg F to achieve the same temperature inside the vehicle.

2. More people die from hypothermia in “above freezing” conditions than any other. In other words, just because you may be able to get the inside temperature to, for example, +35 deg F, does not necessarily mean that one is out of the woods.

(I am not suggesting that we disagree on either of these points, but thought the clarification may be helpful.)