I was out yesterday night working in an unheated airplane hangar, it was about 5 deg F and I was the only soul on the airfield. I decided to pack up and realized that my small radiant heater had almost run out of propane. Well, the car was quite cold by then, cranked slowly, didn't start. Now I'm starting to get concerned. Decided to re-light the heater--nope, it was too cold now for my butane lighter to function. Fingers starting to ache and not work real well. Ruh - roh. I tried the car again and it started. Woo-hoo! My cell phone, my only way to get help, was also cold, I'm sure those batteries would also quit at some temp. It wouldn't have been life threatening: There was a heated storage room in an outbuilding I could have broken into, and I could have built a fire (or lit the heater) using the cigarette lighter in the car to start some paper aflame. But it reminded me to not take for granted that everything will work, to think things through . . . and have some old-fashioned matches on hand.
Lots of ways to get in trouble in the cold when just one or two things go wrong--and 5 deg F is not >really< cold.