Some thoughts, suggestions, good-practices in no particular order. Please feel free to add what I have overlooked
Fill up at 1/2 tank. If you have any EV in the household, consider retaining at least one hybrid/ICE just in case, and keep it at 1/2+. You should never say “I had to stop at the shady gas station at o’dark thirty because I needed gas”. You should never say “damn the storm/earthquake/pipeline shutdown happened right as the fuel light came on in my vehicle what bad luck now I can’t go anywhere”. You also may consider some 5 gallon safety cans of gas with sta-bil or star-tron in them, at home. Gas lasts at least two years treated this way. Beware safe storage and use good quality metal ventless safety cans.
Keep a battery jumper and jumper cables. Periodically check the charge state of the self contained jumper. Get good quality cables, that are expensive, and long. These will be over $100.
Keep drinking water in your vehicles, and warm clothing as he calls for.
Keep some basic hand tools, adjustable wrench/wrenches, screwdrivers, duct tape, gloves, zip ties, even hose repair kits, etc.
Stop far enough behind the vehicle in front of you that you can drive around. If both sides are definitively blocked (18 wheelers, large concrete dividers, etc) stop even farther back so you can move forward within your space to create some distance from someone standing at your window or similar.
Lock your doors as soon as you get in your vehicle and keep them locked.
Consider not having windows all the way down anytime you stop or may stop in an area with people especially pedestrians
Lock your car when it is parked, always, including your own driveway (I even lock our vehicles while in the attached garage just in case garage door is left open, etc)
Check your crash test safety rating of your vehicle, you are far far more likely to die in a car accident than to a violent criminal attack If it’s really about safety, make this a top priority in any future vehicle purchases.
In addition to those crash worthiness tests, bigger is better
Edit:
Trauma Kit! And boo-boo first aid kit. Don’t know how I forgot such a major one there.
Over the last 18 years I’ve averaged over 35,000 miles a year in my vehicle for work.
I’ll add to the list addiotnal things I carry, all the time:
Fire extinguisher(s)
Compressor and tire plug kit
Fully stocked medical kit
Blankets
Spare parts that can leave you stranded, like ignition module, fuel pump relay, etc.
Ammo for your EDC
Knife(s)
Compass and maps
Gloves
Tow strap
Road flares
Water, peanuts, snacks, etc.
CB (not for everyone, but I still have one in the truck and it will always work, even in bad cell areas).
And, if you live up north, full cold weather equipment like heat packs, more blankets, ice scrapers, mittens/hats, etc.
I carry everything listed (plus what Nathan listed) except the cold weather gear, which I used to carry when I lived in Buffalo. I’ve done roadside engine repairs like swapping a bad alternator (auto parts stores will deliver to your location), helped accident victims out, and been safe for over a million miles with this stuff. I can’t tell you the number of roadside tire repairs I’ve done with a plug kit and compressor.
I carry almost all of the above. I also work or travel in remote areas a lot so almost always have a bunch of other stuff including:
Camp stove and a week’s worth of non perishable food and water in my work vehicle. I keep an Esbit stove and a foldable mini wood burning rocket stove in the family vehicle along with a 3 days of energy bars and non perishable food as well as at least 3 gallons of water. Life straw water filters are in all our vehicles.
I have Mylar bivy bags and poly liners for the entire family in all our vehicles and usually at least one sleeping bag appropriate for the season in my work vehicle. Fire blanket to put out engine fire or for shield during forest fire. Rain ponchos for the family.
I also have a machete, folding bow saw and hatchet for road clearing. Bolt cutters both for cutting old fence wire that occasionally can get wrapped around axles and to be able to get through a locked gate or fence if I have to get away from a fire.
If I’m not wearing good hiking shoes (which is rare for me) I throw a pair in the vehicle. Also keep an Atlas for the US and a Delorme Atlas and Gazetteer Topo map for the State I am in.
High powered flashlight, spare batteries, solar charged folding lantern and a very small folding solar panel to recharge phone and flashlight batteries.
Probably some other stuff I am forgetting as well. I don’t travel light;)
My daily commute is an uneventful 50 miles round trip, just a little over 12K miles annually.
But, I prepare as if I won’t make it back due to unforeseen circumstances.
Speaking of back roads, levees in Sacramento are a main concern.
A more common incident is people either not familiar with the area and/or distracted/impaired, leaving the roadway and into the water.
An emergency hammer is never mentioned in any rescue reports.
Forgot to mention the window breaker/seatbelt cutter wedged in the driver side door panel in each of our vehicles:)
Part of my EMT training decades ago was working with a fire crew to extricate people from vehicles. The fire/rescue trainers highly recomended carrying something to get through the windows and cut the seat belts.
You all are mentioning stuff I forgot- hammer (not in CA, Karacal ) Mag Light, and other stuff like binoculars, chargers, towels, and probably a lot of stuff I still don’t remember tha’s in my truck (like a tape measure).
My wife always complains about all the stuff I keep in our vehicles but she is the one that ends up using it the most. Which reminds me I also keep wire, duct tape, para cord and a tarp in the vehicles:)
Yeah I didn’t list everything, if I were to actually empty our vehicles the list would be much longer. But, a lot of the stuff is less critical or is already carried on me anyway.
A dedicated accessible seat belt cutter is something I do not have though…
All of the above for me as well, in addition everyday before leaving, do a pretrip - check all vehicle fluids, all lights, tires, carry spare fuses, extra headlight bulb, spare serpentine belt.
I was going over a pass while it was snowing in the dark when my throttle cable broke. I was on the side of the freeway but just after a turn and in the blind from traffic until they would be right on me. I took bailing wire and hooked it to the carburetor then hooked the twine to it and ran it from under the hood and through the window and tied a stick to it so I could hand throttle the truck and get home safely. So, yes, duct tape, bailing wire, para cord, and some tools are very handy!
Make sure your spare tire has air and holds air and the tools to change the tire.
Another important one the above story reminded me of…visibility gear. Reflective vest, flares, strobe lights, triangles, etc. If your vehicle ends up in operable by a road, you want it to be highly visible.
I prefer real flares to the triangles. I’ve seen inattentive drivers run over or almost run over the triangles before swerving at the last second but pretty much everyone instinctively stays as far away as possible from blazing bright flames. Though flares and triangles are probably a good idea since the flares have a limited burn time.
The flares can also have other uses as well like emergency fire starter and if you have some fire resistant gloves in the bag with them they could even be used to create some space if you get stuck in a crowd.
I tend to agree. I have both flares and some lithium AA battery powered magnetic on one end red/white flashing/strobe things.
I do think it’s easy to kind of not see/subconsciously ignore reflections. We see them everywhere all the time. Road construction things that sit up even when nobody is there, etc…but burning bright red flares are rare and pretty much always mean there are people present (and often LE is present when there are flares which helps people take note lol)
Spare belts are a very good idea especially if you are traveling in rural areas. Even if you don’t know how to change them yourself you can usually find someone who can but the parts could take a couple days to get there.
Another item I forgot - siphon hose with brass bobber. Allows you to get gas out of tanks without having to risk getting a toxic mouthful. Could also be used to get water out of shallow wells or tanks.
and riding 
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