Winter can be brutal, merciless, and annoying. Last winter ('13-'14) was my first time driving in the snow in over four years. And since I only learn by making mistakes, I learned quite a lot.
Everything in this list is from personal experience, my personal opinion, and from repeatably getting stuck on the side of the road with no power (personal best, an hour and 10 minutes in 10 F!). I also added some pics from last winter where I hit a patch of black ice and spun off the road. Because I know you guys love to see PT Cruisers abused.
This list is by no means a final draft, so use it as a jumping point on what might be the best for you. It's really meant to get the gears in your head turning.
So here it is:
Make sure you are properly clothed, aka bundled up. I [mostly] always walk out my front door with a hoodie, winter jacket, a hat, and a scarf. You might of noticed I didn't mention gloves. That's because I just keep them in the car at all times. I have also begun wearing boots while driving and just switching to my work shoes once I arrived. Yes, I know the car is warm, but what if you lose power? Or have to go outside of the car? Being in the cold for long periods of time really affects you.
If you can fit it in the vehicle, keep a shovel inside the car. I always have a seat down so I can fit it in the car. You want to use the shovel in case you get stuck on a small snow pile, or you went into snow too deep. You can just shovel the snow away.
Ok, let's say you're stuck in the car until help arrived, so make sure you keep blankets in the trunk/backseat. Trust me on this one. When I was stuck on the side of the road, with only a winter coat to keep me warm...just...never again.
The next item is an odd one, but is/can be very crucial, bring a pop bottle with you (or for all you conformists, a soda bottle). If you are stuck for a long time, natures call will happen. From personal experience, a 22 oz is a excellent size for this. But it's only good for one go (top it off at your own risk!). Since the small size fills up quickly, it also makes a excellent hand warmer! When you have no blankets, it is a welcomed source of warmth. Note, I used a Mountain Dew bottle, which has deep treads around the cap, because of it being carbonated. A water bottle doesn't have those deep treads, just a fyi. You can use it, just be wary of spillage. Just....don't expect a desposit back if your state does that, :p.
Keeping food in your car is a great idea as well. I personally do not because I'll be commuting home and decide I'm hungry and eat from the stash. If you can refrain from doing that, good for you!
This next one may seem obvious but I will mention it anyways, Jumper cables. Sometimes when it's so cold outside, the car doesn't want to start for whatever reason. It's like the car is being lazy, so jumper cables can be the middle finger you're giving it to stir it from its slumber.
A long flathead screwdriver. This one is an odd addition but hear me out. Last winter was so cold, I had to put a heater above the engine block to heat the car up to even start it up. This is when I discovered that my hood was frozen shut. I believe most cars have two latches for the hood, one you can open from inside the car, and another that you open manually from the front. On my car they were frozen shut, specifically the springs were frozen. I had to get a long screwdriver to jam it in there, to pry the sucker open. Of course I view paint scratches as war wounds, so results may vary.
If it's dark, a flashlight will be helpful. Actually, two flashlights would be better. One that can be set on the ground and one that you can stick in your mouth to hold (for the aforementioned screwdriver idea). You need to see what you're doing, right?
Keep a phone charger in the car. Whenever I go out, I always plug in my phone to charge, even if it's at 99%. I could care less that it might slowly kill the battery. My logic is this, I need the phone to be as charged as much as possible, so I can have it for emergencies. Also, waiting in the car is really boring, so I can surf the web as well. But it's mainly for emergencies.
It's a good idea to keep Heet in the car, just in case. What happens is this, (as it was explained to me) the colder it gets, condensation will occur in your gas tank. The closer to empty you are, theres more room for the condendation to occur. It basically prevents the car from turning over. Heet, using science and witchcraft, removes the water from the tank or something....I have no idea how it works, I just know it does.
Technically though, I usually never get a chance to use Heet because I aim to make sure my car never goes below half a tank. If you're like me, and commute ~40o miles a week, you'll quickly notice that you'd be visiting gas stations every other day. It's a small price to pay, especially when you car gets 24 hwy mpg. But at least the car is still functioning, right?
Of course, this is all that I can think of at the moment. If you have more suggestions, leave them in the comments please. As Red Green always said, "we're all in this together".