My Jeep and 3/4 ton truck are stocked with enough tools to almost build a new home or drop an engine.... but the wife's car... that had to be well thought out. We're rural, cell phone signal not always available depending on where you are.
My wife drives a PT cruiser btw and as a certified accountant travel to clients out in the booneys off the main roads a lot. She'll sometimes use the Jeep but preferes the car since I haven't modified it any way - yet (unlike the Jeep or truck)
- portable air compressor (Coleman-long life type) for tires and kids toys (balls and beach toys)
- replaced the spare tire screw down mechanism with rubber bungee cord - the screw types sometimes rust making spare tire removal all but impossible
- replaced the factory jack with a small hydraulic one that's easily female operated and welded a plate to the top of said jack to help make it less rocky.. bungee corded to spare with it's handle
- a real four way tire iron - we experimented until she understood that she can stand/jump on it to loosen a wheel nut. No weight jokes
- a giant size can of tire inflater and sealer (will do a 17 inch truck tire, I figure she can get enough of that in to blow up her car tire and seal a hole if needed)
- A Canadian Tire brand portable 700amp booster pack with inverter (stops wife from opening the hood to assist others) will charge from rear hatch 12 V outlet.
- complete first aid kit industrial type (I got it free when I worked at the brewery) always keep it fresh
- a breakdown camp shovel and a bag of salt (self explanatory here in snow country)
- a set of those super bright LED warning tripods truckers often use (I won them in a raffle at the school)
- a tool kit of the style you often find on sale for ten bucks imported from China and a pair of gloves
In winter there's always a blanket in the car for my son just because he likes it.
Since we keep our vehicles in good shape, we find the gear is more often used to help others than it is to help us. But that's the point, just being prepared. Notice there's no booster cables, only the booster pack. Of course, I have booster cables ... lol...