Here in Iowa, our center goes to the local feed store and buys 50 pound sacks of "CHICKEN GRIT" (laugh all you want). All the package cars have a large sealed bucket with about a sack and a half of grit in it. If by chance you get stuck, all you have to do is a few simple steps and you are going again.
First, Kick out a little of the snow from in front and back of the FRONT TIRES.
Second, Kick out a little snow from in front and back of the REAR TIRES.
Third, Spread out a trail of CHICKEN GRIT in front of the REAR TIRES.
Fourth, Put some CHICKEN GRIT in the rear tread of the REAR TIRES.
Put the package car in 2nd or 3rd gear and let the package car lug it's way out of the slick spot and you are off and going.
I've been delivering for close to 30 years and have not had a wrecker on my package car yet. I drive a P1000 over 225 miles a day with close to half of those miles on secondary/gravel roads.
The key to safe winter driving is : If in doubt........Don't do it! If you think it looks like you are going to get stuck going down some unplowed road, DON'T GO DOWN IT. If a dock is snowed in, don't back up to it. ALWAYS park your package car so that you can go forward or back so you can "rock" the truck a bit if you need to get going.
Hope this helps.