With great plains blizzards one of our biggest hazards, and with the possibility that I could become stranded far from a town and (in a white-out) find it impossible to safely reach someone's home, my car kit includes, in addition to what you listed:
High-energy foods (candy bars, peanut butter, etc)
votive candles - provides heat and light, I buy the long-lasting kind
blankets (regular and "space" blankets)
some fluids, but snow can provide a lot and packaged fluids freeze, anyway.
sealable baggies (for bodily function waste)
Several cans to heat water, scoop snow, etc.
older but good cold-weather gear (gloves, scarfs, hats, etc)
30 foot snatch rope (big thing, made for pulling cars out of a ditch, it "springs" after tightening and "snatches" the pulled vehicle loose. Hooks on both ends).