Good list, especially when you add in the other "standard items" to have in the car.

The only thing I would suggest is that things like the down booties, mittens, sleeping bag are one per person.

If you are traveling with family or a car pool (to or from work), you will need to think about dealing with the group. One thing the occurs to me is having a large down comforter or wool blanket. You could then cover everyone in the back seat, for example. Maybe some cheap $ store gloves and knit caps too. Something is always better than nothing.

If it is you who are riding in the car pool, you may have to make your own plans.