Some of the comments got me thinking about this topic. I covered this years ago on another forum.
For many years I was a member of Buffalo Creek and those that have been there can tell you that it is out there. I used to go all the time in the winter and was always prepared for it. I will say that I do have different supplies in the car and truck as does the wife in her van. The car does not make back country trips on Forrest roads in the dead of winter but the truck does.
Basic supplies in every vehicle.
First aid kit
small basic tool kit with wire, duct tape, tie wraps, jumper cables.
1 MRE with heater (changed every year)
1 blanket
1 space blanket
chemical hand warmers 3 pair. (change these every year)
3 road flares
LED flashlight
Spare batteries
Pair of gloves
cheap plastic poncho
some paper towels
1/2 roll of toilet paper in a bag
2-3 bottles of water
couple of plastic trash bags
1 can fix a flat
Due to the nature of where we go in the truck in addition to the above.
another blanket and space blanket
sleeping bag
2 more MRE's
coffee can
candles
fire starter, lint/Vaseline
tire plug kit
air pump
tow strap
fold up shovel
more hand warmers and water
compass and topo map of colorado
And some more things I am forgetting right now but ya get the idea.