Car Safety Kit

Bag: You can buy ready-made plastic emergency kits that have compartments, but a bag is handier because you can stuff it away in a corner, something you canít do with a rigid box.
Jumper cables: A pair of high-quality jumper cables. The heavy copper wires are black (the negative side) and yellow (the positive ďhotĒ side) and terminate in color-coded clamps.
Flares: Emergency flares, If youíre going to carry flares, buy a half dozen of them and practice lighting a couple before an emergency happens. Itís tough trying to read the instructions that are printed on the side if there really is an emergency and you want to warn oncoming traffic. Some experts like foot-tall reflective triangles that are set up down the road from the site of the problem, but nothing attracts the attention of oncoming traffic like a flare.
Shop rags: We keep a couple of genuine shop towels in the bag and while old wash cloths and other rags will do, shop towels seem better suited to the job. The red kind can always double as a flag if needed so you can attach one to the occasional long item that you bring home from the hardware store. You can buy a dozen or so for a couple of bucks. When they get really greasy, recycle them.
Ice scraper: Even in California, you sometimes get cold (to us), frosty evenings that coat the windshield and turn to ice the next morning. You can get an ice scraper that is electrically heated and plugs into the cigarette lighter. 
Tire Inflator: and/or a can of pressurized flat fire sealer. Some are not totally in favor of the can stuff because it might tend to put the tire out of balance. Read the instructions carefully before you buy it and remember that itís recommended that you pull out the nail or what ever before you install the stuff. 
Tool kit: That last suggestion means that youíll have to include a pair of pliers in the bag to do the pulling with. It contains the pliers, two screw drivers (large and small bladed and capable of being converted into Phillips drive) and a tire pressure gauge. A hammer a couple of adjustable wrenches.
Bungee cords: These are the kind with metal hooks on each end. Keep a couple of them because one isnít usually strong enough to hold things tightly.
First aid kit: 
   
Q-tips in a small zipper case.
    first-aid cream for minor burns and cuts
    Assortment of adhesive Bandages
    Extra large to pinkie-sized
    Antibacterial ointment
    Aspirin free pain killer
    Antiseptic towelettes
    Roll of 2-inch gauze
    Roll of bandage tape
    Instant ice pack
    Sterile eye wash
    Tweezers

    Safety pins

Work gloves: Leather-faced cloth work gloves.
Gas can: A small (about two gallons) plastic gas can filled with drinkable water. If you are using an older can you can try to clean it by rinsing it out toughly with a little bleach and water. 
Other
Plastic garbage bags
Heavy work gloves, preferably leather, kitchen or surgeons gloves with those silver reflective glove liners inside)
Blanket
Flash Light
Change of clothes
Flares
Rope

What will you need for three days if you are stuck on the freeway--or even on a bridge?
Water and food for three days that doesn't require cooking, a source of caffeine (if you are an addict--this is not the time to do withdrawal); it's also nice to have something warm to drink.
If you have room, a small cook kit would be ideal, even a Sierra cup and one of those tablet fuel folding stoves.
You will need warm clothes, hat, gloves, plastic produce bags to put over feet (inside your shoes) if they get cold or you are walking out in the wet.
Plastic garbage bags, heavy work gloves, preferably leather, (if you have work to do that requires finger dexterity, cold, wet weather can be painful--try kitchen or surgeons gloves with those silver reflective glove liners inside), blanket, or space blanket.
First Aid Kit, prescription medications you need daily glasses or contact lens care, dust masks, safety glasses, mouth to mouth shields, waterproof matches. Those trick birthday candles work well for fire starting as they don't blow out and are very small to pack.
Fire extinguisher, flashlight and extra batteries, battery radio (don't use up your car battery listening to the news).
Sturdy shoes and socks in case you need to walk anywhere, a day pack to carry your stuff in if you do set out on foot (try the thrift shops for sport bags and day packs).
A note-leaving kit to tell those who find your car where you have gone and how you are (post-it notes work well - write on the Back and stick on window).
Be sure to have your identification, emergency phone numbers and information with you as well as family pictures, their license numbers and car descriptions in case you need to search for information about your loved ones.
CASH in small pieces and change in case the phones work.
You should have a compass in the car and local area maps (landmarks may be changed, signs downed; and you may need to chart a new course home that does not involve bridges and overpasses... uh well, except for a few big bridges in some parts).
A Jack knife, flares, maybe a tow rope, some tools, camp shovel and an ax.
I carry a wrecking bar bungeed under my seat to bash my way out, or into someone else's car that has become a trap.
A poncho for improvised shelter outside your car, rain, or privacy when nature calls.
You might want to tuck in a margarine tub with plastic baggies. You have to store the TP and handiwipes anyway.
If you will have a baby with you, diapers, plastic bags, baby wipes, and food.
And after a day or two, you'd kill for a toothbrush and paste.
Lip balm and hand cream help in the weather.
It's nice to have some comfort food goodies stashed, maybe a deck of cards, a good book. It will be a long three days.
You need enough of ALL THIS STUFF to equip or feed the number of people who are likely to be with you at the time. If you will have the dog with you, you'd best stash some dog food and count the dog as a person in your water needs.
Now, as for food.
The 2400 or 3600 calorie energy bars provide nutrition as well as energy. They have a long shelf life and can handle heat and cold in the car. You could make 3600 calories last for three days. You probably won't have room but you can get MRE's (meals ready-to-eat) at emergency suppliers, the camping supply or army surplus. They come as complete meals with entree, fruit or dessert, crackers, beverage mix, utensils and napkin. Or try the new nutrition drinks. You can do great things with Vienna sausages, Deviled ham and crackers or canned brown bread, can opener' granola bars, boxes of juice.
The trick is going to be water.
That's the thing you can't live without. Best are the water packets with the 5 year shelf-life. They fit into small spaces and adapt to the space you have. I stash 2-liter bottles of it under the seats in my van; put 2 or 3 in a plastic bag so they don't roll around and secure with a small bungee cord. One-liter bottles fit in the storage compartments on the sides in the back. In a compact passenger car you can get a couple of 2-liters in the tire compartment. Then the flexible packs are best for stuffing around and into the spare tire.
All this stuff in a car?
Actually, it can be quite compact if you're careful and use your nooks and crannies well. Remember this is Emergency stuff; it doesn't have to be handy.
Look for compartments: pop up the back seat in your sedan if it isn't part of the trunk, use your spare tire compartment to the max, string hammocks at the top of the trunk space where you don't use it. I had a problem with my husband removing any sport bag of supplies I put in his trunk to make room for luggage or someone else's golf clubs. It's better to break things up and put them where they won't be in the way and hence, removed.

Store things individually: jackknife and matches in the main ashtray, compass and extra batteries in another ashtray, soft gloves and hats in the flexible saddle bags on the back of many front seats, space blankets or bags in the map compartment in the doors. Put socks on your water bottles, cram individual soft things in between stuff in your cubby holes. For comfort, you can lay a blanket out flat in your trunk inside a flat garbage bag or in the back of your van, perhaps covered by a piece of carpet to keep it clean and in place.

I've considered making a hanging bag of stuff to feed into an empty space behind/below another small ashtray. Hang hammocks of things under your seats with bungees or cord tied to the springs so they won't be kicked out.

Consider these supplies a base for your home supplies. If you are home, your car is likely to be also. It can be a source if you must escape your home. Consider a hide-a-key to get into it if you can't grab your bag; stash a house key in the car to get back in your house in the same event. Remember, you are on your own for probably at least the first 72 hours. The Red Cross will not have coffee and donuts at the next corner and the National Guard will not bring you water.