Excellent discussion. My car has been well outfitted the past few years (especially in winter) including Gore-tex hiking boots, Smartwool socks (stuffed in the boots), long underwear, several pair of gloves and mittens (which gloveless friends have appreciated), fleece neck gaiter, balaclava, fleece hats.

One of my favorite layers in the car is a Marmot Dri-Clime vest. Campmor often has a great price on them.

New to the car this year: down booties. I had three pair in the house and decided a pair would take minimal space in the car and would be such a blessing if stranded.

And while not clothes but useful for putting in clothes: chemical hand and toe warmers. Costco sells them by the box.