I pack a skidoo suit, think a sleeping bag that you can walk in. Mitts ( insulated snow mobile style gloves are ok too ), snow boots and liners, toque and scarf. I have slept comfortably in that, + a sleeping bag, in -40 in a VW Rabbit. Have a couple of 6 cell battery banks for charging cell phones. Winter sleeping bag. Catalytic hand warmers and lighter fluid. Most of that is in a hockey bag that lives in the car all winter. There is an all year kit too, smaller but has the first aid kit and more food and tools. Also a stainless steel bucket. Shovel, air compressor, spare tire, tire plug kit, a gas stove and tanks, camping cook kit, dried food. Strap on pouch for insulin etc. to wear inside the suit.
If I'm traveling I also probably have a day bag.. change of cloths, spare socks, money, passport, first aid kit, flash lights, 2 meter HT, batteries, chargers, spare laptop ( it's me after all ), mini GPS ( charges off the same USB battery banks )
And then there is the stuff in my pockets and belt .. Cell phone, single cell battery bank, Flashlight ( same battery as in the bank ), knife, lighters, magnets, keys, USB drives, 3" wrench, diamond file, pens, paper, dosimeter, one ounce hand sanitizer, tire pressure gauge, insulin pens, test kit, driving glasses, reading prescription glasses, contacts and reading glasses. Yes I have large pockets and wear a denim jacket.