Some of the most critical items in a crisis take up very little room in the car and aren't a big financial hit if Mr. Goodwrench steals it at the shop. Such as:
Bic lighter
Matches
firestarters (cotton balls and petroleum jelly)
stainless cup
bottled water
garbage bags (serves as poncho, tarp, pack cover, etc)
old knife
aspirin, bandaids, First Aid kit, cotton bandannas....
I have these things in seat pockets, door pockets and other nooks and crannies.
I've done a lot of camping, including sleeping in the car (Honda Element), and based on those experiences I keep in the car at all times (even when at the Honda dealer), fleece sleeping bag liner, Smartwool socks, long underwear, Marmot Dri-Clime, waterproof parka, fleece hat/neck gaiter/gloves and an old pair of Gore-Tex hiking poots.
In the winter I add an old pair of down booties.
If I lived in NH I'd have some warm stuff in the car all the time. I do in DC most of the year.
I've been camping and collecting gear for twenty years so have plenty of old stuff which would not cause me to lose sleep if it were stolen and would allow me to get some sleep, and survive, if stranded.
For the winter I also have an old JetBoil stove in the car and I keep several packets of Lipton's Cup 'o Soup in there as well as cocoa and a few other food items which would be lovely if were stranded for more than a couple hours on a cold day.
Seriously imagine being stuck in your car without a heater for a couple hours in January....