Always a good idea to remind everyone about winter safety kits, and the importance of carrying one if you live in the more treacherous regions. After all, it took me two snowfalls to remember to put the ice scraper back in my trunk for the season. (Thankfully, winter in southern New England is usually more annoying than dangerous.)

Also worth mentioning: if you're thinking about keeping food in your trunk for emergencies, head to the local supermarket and check the clearance bins. You can usually find a couple wrapped-but-unboxed Powerbars (or something) for a dollar or so. Pick up a couple and stash them in your car. While they won't warm you up like a hot meal, they're nonperishable and give you a quick energy boost.

You people with remote starters and the engine block heater option can just carry on with your lives.

Ok, while a good start, those of us living in real bad situations need more.
I've been living in the middle of nowhere, up here in upstate NY south of the lake for my whole life. I've had my share of winter experiences, accidents, hiking, etc. Even including walking miles to a working phone. Lake effect here is no joke.

First, I can tell you that the trunk of a car isn't the best place for a lot of things. If you get stranded, or in a spot where you can't get to that kit in the trunk, and you can't fold down your rear seats, you're sunk.

Now, additional items to think about or change.
Chemically activated warmers. Those little heat packets in the hunting/sporting sections that will heat up if activated. Cheap, reliable, quick heat if you need it.

Jump pack. No excuse why you shouldn't have one. They make ones that have AC converters, air pumps, USB outlets, all in one.

Flares. Either electronic or traditional. If you are stuck in a ditch, and can't get out, the last thing you need is someone mis-judging the same corner you did, and running you over.

Shovel. They sell small plastic ones that extend out. Good if you're stuck but can possibly get your way out.

First aid kit. Reasons should be obvious.

Battery powered strobe, or some other emergency light that blinks. Will catch attention of passers by if you're stuck, warns other drivers to steer clear.

Tow strap. Even if you're not stuck, you might help someone who is.

Jug of ice melter. Good for getting off ice, or giving you traction in some cases.

Fire extinguisher. (Especially if you're carrying camping gear/propane/etc.)

Washer Fluid. (You always run out when stuck behind a big truck spattering you for miles on end it seems)

Extra quarters. (For pay phones, air pumps)

Notebook and pen. (If you have to leave your car, write down contact info.)

Spare key. (On you, obviously. Last thing you need is to lock yourself out of your car in sub-freezing weather waiting on AAA or a locksmith).

A pill bottle containing 2 doses of any meds you are on. I actually have a more flat shaped "pack" I carry with me that has my Rx meds, as well as a few OTC ones. (Do not leave in your car. Carry it in your jacket, pants, etc.)

Caffeine pills. Shorter days mess with your sleep cycle, and sometimes you might feel tired and need a jolt, but aren't near coffee.

Warm hat. You lose a huge amount of heat through your head. Preferably one that covers your ears.

Obviously, a cell phone. But also remember a charger.

AAA card. In my case, on our gold family plan, its more than paid for itself in just one tow.

Additional prep ideas....
Make sure you keep your door seals coated with a silicone based spray like armorall or even better black magic. Keeps any moisture from sticking seals together and icing your doors shut. Also remember to spray your tires. The cold, plus salty roads dries out the rubber on the sidewalls.
Spray locks and hinges with graphite spray to keep everything from getting stuck.
Make sure you can turn your lugnuts with your wrench. Last thing you need is a flat, and you can't even budge your lug nuts to put on the spare.
Bring an assortment of music. Even if you normally listen to high tempo rock, have something that calms you. The last thing you need while driving in bad slippery conditions is fast tempo music that amps you up and makes you anxious. You want to be aware of conditions, and be able to react quickly, but be calm and drive in a laid back state.
Last, I think.. if weather is gonna be really bad and you have to go somewhere, let someone know where you're going, and when you expect to be back. Make a travel plan and stick to it.

Above all, use common sense. Drive slower, counter-steer into skids, don't brake in the middle of a turn, make your moves smoothly instead of quick corrections. And watch the weather. Just because it looks fine out your front window, doesn't mean its not a blizzard where you're headed. The best tool to have is up in your head. If you drive smart, most likely, you wont need anything else to save your stranded ***.

great additions, I was actually coming on here to add many of those same items. I keep much of what you listed in my vehicle at all times, I can be anywhere from the Canadian border in Northen Maine, running along the Great Lakes, or down to Texas any given week so I like to be prepared.

I'm glad you added fire extinguisher, you wouldn't belive how many times that has come in handy not on my own vehicle thankfully but you never know. I keep two, one in grabbing distance from the driver seat and another in the cargo area. Remember to have them safely mounted so that should you get in an accident they don't become projectiles in your passenger cabin.

On the subject of tow straps, remember, in a pinch you can lay them out for a surface to grab traction on. And yes, they are good to keep in your car even if you aren't in a vehicle that can pull others out of a ditch.

and Kitty Litter- forgive me if it has already been mentioned and I missed it. A great thing to put down for extra traction. Get the cheap old school clay.

I'm with ya on the fire extinguisher. I made a special mount for the ones in the Cruiser, one in the back compartment, and one on brackets mounted just underneath the drivers seat. I have one right behind the seat on the LeSabre, not sure where I'd permanently put it that isn't in the way.
If not for your own safety, but maybe someone elses.
Back at an old job, I was driving home on just normal rainy interstate roads. I had a guy pass me on the highway with a donut spare on the back. Doing 70mph. Well, fast forward about 10 minutes, and I round a corner to a cloud of fog. Not sure what it was, so I slow down. And I just barely could make out the guy that passed me in the median. He had blown out the spare, spun around, and pinned himself under the guardrail all the way up to the windshield. Leaking fluids everywhere, and he was still in the car. I pull off to the side, but back up a little and put my blinkers on. Grab my fire extinguisher and run to the car. The guy was disoriented, but otherwise ok. I call 911 and they sent out a cop and a fire truck. Meanwhile I get this guy away from his car, stick out a road flare back aways, and try to calm him down. Let him use my phone to call his parents and let them know what happened. He was pretty lucky. I didn't have to use it, but if just a little fire had started before I got there he woulda been in big trouble without it. And I see the little designer ones in colored bottles that the ricers stick to the a pillars. Those are worthless. I have 2 medium sized ones, specifically rated for automotive situations. One may not be enough.
I also carry a handheld CB. In our area, we just recently got cell coverage (just this May AT&T put up towers here), so I had that with me as well. We were in a totally dead cellular zone before that. So in this area, tons of people listen to scanners, and lots of people still have CBs. So it makes sense to have one if you don't have good cell coverage. Better still, would be to have a HAM and a license.
I used to have a full Midland CB back when I had my trucks. I don't think a 7' whip on the LeSabre would work out though...lol. The bank drive thru always hated me for that. I'd usually get out and walk in if I had the whip on the van.
And modern GPS is a great thing to have. No second guessing where you're going. Plus easier to find a garage, or medical facilities, or the nearest gas station is, if you are traveling out of your home area. Which also brings up the point to keep a nearly full tank of gas. Traveling around on 1/4 tank isn't smart. If you end up stranded, that 1/4 tank isn't going to keep the motor running for long, and with power outages shutting down gas pumps, you don't want to run into that problem. You don't want to be running on fumes looking for the next working pump.

damn scary dude, we think alike lol I was just thinking of mentioning the CB. I always have one in all my vehicles. Coming from a line of truck drivers it'* just second nature to have one. Nowadays there'* a bunch of yahoos on 19 but it'* still a great way to get an ear on info for road conditions.
Plus there are still some rural areas that monitor channel 9 for emergency calls.

I'd like to add the unopened short pint of Scotch and Pack of Marbs/matches I keep in my trunk accessory bag. Just in case you are truly stranded.

hey im sure its been mentioned but a spare tire is a must..lol i just came home..on my way(in the wife truck) we stopped to gas er up for the week and i got out and hear a hissing..chrouched down and found a damn razorblade sticking out of the tire..glad it had a spare and a jack..glad we werent in my truck as i have no spare haha...not sure it wouldve taken my tire so easy but it could have..anyways the point to this is to not be wearing jeans that are ripped down the back as my *** is frozen now haha from the cold wet concrete..here is a pic of my jeans...

This is where a tarp would have been nice

that is very much so true lol

If you drive a RWD GM vehicle I suggest a spare alternator, qty 2 13mm wrenches and a 3/8 breaker bar.

We have had 4 of these alternators go bad without warning in 3 different Bravadas and a K2500. Very easy to replace on the side of the road, but will strand you fast. In the case of the Bravada, if the alternator fails and battery drains, and wife happens to put it in park while in a intersection, vehicle will not allow movement back out of park which means a towtruck to move out of intersection (or battery swap while people are honking horns wondering why you don't push it out of intersection).