I watched a video of "the Survival Mom"
http://thesurvivalmom.com/ but the link to the video was bad so I can't give it to you.
Anyway, she talked about the categories of things for moms to always keep in your car.
She called them "the five S's": Sanitation, Sustenance, Survival, Security, and Sanity.
She ran out of time on the video to talk about all of them, so I will just wing it from here on, with stuff I came up with in those categories.
(My ideas)
Sanitation:
To wash hands- a clean sodapop bottle filled with water, some paper towels OR a package of WetWipes.
Do your kids get motion sickness? Carry extra large paper cups with snap on lids. Extra clothing.
Potty problems: extra underwear for your little kids, diapers.
A way for your children to go to the bathroom. Does your toddler need his potty seat?
Toilet paper (the Survival Mom showed some TP she had taken the cardboard tube out of, and then sealed inside a Vacuum Sealer bag for longer term storage.)
Sustenance:
Moms know that they need some food in the car for every day emergencies.
The hotter your climate, the shorter your food will last in a hot car. She suggested only keeping things like hard candy.
Another option would be to have a small totebag of snacks that you carry in and out of the car each day in the hottest months. This would keep the food safe longer.
Another option is to rotate the food quickly. Only put in enough granola bars or juice boxes for the next few days.
Bring LOTS OF WATER. She keeps a couple of sodapop bottles filled with water under the back seat. also a case of commercially bottled water.
Bringing water in the car with me has been one of the best habits I have ever had. With 6 kids, I used the water to clean them up, to refill the radiator, and to drink. It was a lifesaver.
Survival:
The only thing I heard Survival Mom say about this one was to keep good walking shoes and socks in the car for every family member. She said if your car breaks down, you need to be able to walk.
I recommend having a flashlight, matches, flares, camping knife, cell phone charger, maps, and big pieces of paper and markers to write a message to passing cars.
Security:
If you don't have a concealed carry license, maybe you want some pepper spray, mace or bear spray (whichever one is legal in your state). Even wasp/hornet spray that shoots 10 feet would work if you need to spray some attacker in the face. I even saw a self defense show once that said to put your auto fire extinguisher up to the window and spray out the window into the attacker's face. That little bit of knowledge makes a fire extinguisher even more useful.
But of course its better not to get yourself into a dangerous situation. Keep your cell phone charged, learn how to change a tire, keep your car repaired. Always let a loved one know where you are going and when you are going to be back.
Sanity:
For kids, you need something for them to do.
While driving: Don't you just love those DVD players?
While stopped. If your vehicle is in a traffic jam, or it is broken down, or if your errand requires you to sit in a waiting room for hours, keep toys, gadgets, books, snacks, etc. ready to go. That will save your sanity as well as the children's.