Well, you said emergency survival and winter. One book I think is a great resource is Cody Lundin's "98.6 Degrees: The Art of Keeping Your Ass Alive." The book itself is (probably) too much information for them. However, it's some of the most basic, ground-up good (and clear) explanations of the basics of survival.

Based on what Hug-a-Tree and Lundin say about events that turn fatal, avoiding hypothermia and being seen/heard is going to be what's most important. Lundin's book makes it really clear the ways you gain heat and lose heat (convection, radiant heat, etc), and ways to counter the loss and increase the gains (he shows the opposite for a desert/hot environment).

So, showing the boys what are the things that will make them dangerously cold and how to counter them (how to get yourself off the ground, how to insulate themselves, etc). So perhaps show traditional ways to stay warm - tent, air mattress, sleeping bag) and how to improvise/McGuyver it and get similar results by working with what might be available to them.

And I like Les' idea of letting them test in cool to cold weather how much a hat (or lying on the ground vs. lying on insulation, etc) affects how cold you feel.