My wife and I dared each other that if it ever got below "0" we would both streak one lap around the house wearing nothin but rubber boots.
Well, it plunged below "0", so we ran around outside the house. She went in first and locked the door. I stood there for an entire minute before she opened it up. She thought it was sooo funny.
That was the longest shriveling minute of my life.
Just a tip for those storing the warm stuff in the trunk. Move to the passenger compartment for actual driving. Lots of cases where one could not readily reach warmth when needed.