Here's a PARTIAL winter list I'm sure others will add to:
For the engine:
Antifreeze: a 50-50 mix of water and antifreeze fluid is best, protecting down to 35 below zero.
Battery: auto batteries love to die when you need ‘em the most. Make sure posts and connections are free of corrosion and are not frayed. When temperatures drop below zero, even a good battery’s power level drops by 50%. If older than three years, have your battery tested at a certified facility.
Oil: Change engine oil to adjust the viscosity grade. The colder and dirtier oil is, the thicker and more sluggish it will be. Thinner, cleaner oil will put less stress on the battery and starter, as well as conserve fuel. Check your owner’s manual for the correct oil for the temperatures you anticipate.
While you’re at it, make sure windshield wiper blades do their job and the washer solvent is topped off and won’t freeze. Also check all belts and hoses under the hood for wear and proper tension.
Fuel: Keeping your fuel tank as full as possible, never below half, keeps condensation (water) in the fuel system to a minimum and provides fuel for emergencies. A full tank can maake the difference between life and death when stuck in the cold.
Other stuff:
Tires. Consider changing to snow tires in winter. They’re not magic, but they provide better traction in mud and snow. Tire pressure changes in the cold, so keep them inflated to manufacturer’s specs for best traction. In Montana, Idaho, Washington, and Oregon, road authorities REQUIRE chains to go over some mountain passes. I’m sure other places have similar regulations. You need a set for each power axle, and if you don’t know how to put them on and take them off properly, then don’t drive where they are needed.
Carry a winter emergency bag inside your car. Okay, so it’s more junk in back, but this is a case of better safe than sorry. Things you absolutely MUST have:
* Blanket, coveralls, coat, and gloves. In an emergency, put warm clothes on FIRST!!
*Flashlight, flares, and first-aid kit.
*Snow brush and ice scraper.
*Jumper cables and basic tools, including an ax and snow shovel
*Containers of extra food, water, and matches.
Other things I personally never leave home without:
*a text phone with numbers to call for help on the speed dial
*a waterproof tarp
*a down sleeping bag rated to 20 below zero
*a .22 with a brick of ammo (If you have to ask what a brick is, you probably won't have the gun along, so don't worry about it)