Beside the obvious things: checking fluid levels, getting tune ups, making sure tires are safe and filled, and having enough gas, this may sound silly and you never think it will happen to you, but if you are in extreme weather regions, pack your vehicle up with things you think you never need:
Extra clothes: gloves, hats, scarves, pants, coats, sweatshirts, heavy well made socks for warmth/walking, blankets/comforters. Extra boots or good warm walking shoes. Pack for a few people, you never know who may be with you or who else you are able to help.
First aid kit: along with meds you need or that may help others. Along with the kit, I have Ibuprofen, Tylenol, Albuterol inhalers, Pepcid, Anti-Nausea, Imodium, Tums, Epinephrine pens, band aids, alcohol wipes, diabetic tabs, hard candy [for diabetics], cough drops, pain killers, Benadryl [25/50 mg will stop a severe allergic reaction from worsening until you can get to an ER], plastic CPR mouth to mouth face mask. Twine, a good leather belt can be used to drag things, pull things and as a tourniquet.
Food: Bottled water, energy bars, healthy non perishable snacks/food.
The Vehicle: wiper fluid, oil, transmission & brake fluid, anti-freeze, jack, jumper cables, gas can, tire iron, spare tire, a one shot unit for battery charge, air & power, rags, sand paper [used that to clean off my battery clamps], kitty litter/sand, [if stuck in mud or snow put under the tires], rubber gloves [used these to get a stuck lug nut off a rim], flares, lighters, stick matches, old newspaper/magazines [you never know if you need to start a fire to keep warm, the thin wooden flats to mix paint work good too], cardboard [to lay on if you need to get under your vehicle, also can be used to put under a tire if stuck in mud or snow, as well as for a fire], tools [good socket set too], scissors, working flashlights, rock salt, plastic tarps, garbage bags, small plastic bags/various cloth bags/backpack.
Toilet paper. If you have a portable toilet, that too.
Communication: cell phone charger [there are solar powered ones now too], extra cell phone fully charged [I have an old cell, that simply dials numbers for emergency], reading material, music.
My battery decided to simply quit and I had to wait over an hour for roadside service due to everyone that needs help [this day some people waited over 8 hours.] This was in about 10 degree F weather. I was unable to put the heat on due to not being able to start the car. There were no people in sight to help me with a quick jump.
After that experience, I put all these extra things [I already have tons of things in my Jeep already] just in case.
If you have roadside, use it. If you do not have roadside, get it. Use your vehicle owners manual if you are unsure of a warning light, what kinds of fluids your vehicles needs, how to change a tire, they have everything you need in there. Most times, you can fix something. If you notice your vehicle acting strange, stop, pull into an open store parking lot if possible. If home, do not go further.
If you see someone stopped/stuck/stalled in a vehicle or walking in awful weather, especially with children, just pull over and ask if they are okay. If you do not want to pull over and see someone definitely struggling, the least you can do is call 911 so they can get some help.
You can always help someone else. There have been numerous times strangers have helped me, so in turn, I always at least try to help back. You do not have to get personally involved, you only need to pull over and say "Are you okay?"
If anyone has more suggestions, please do let me know.