We have been over thinking this...Fortunately I am a fan of "Prairie Home Companion" and they discussed a much simper solution in a presentation called "Living in the North."

You need only a rifle and a knife. When stranded, you shoot a passing bear, disembowel him, and huddle inside the warm carcass until help arrives. Takes up less space and no nitpicking about down vs, synthetics, etc. Also, no issues with carbon monoxide and all that bothersome stuff

I wonder if a buffalo would serve as well s a bear.....