Two ice scrapers - My dad taught me to always carry not one but two ice scrapers in my car. One for me in case of ice, and one to give away to the poor soul trying to use a credit card two spaces down from me.
Two umbrellas - Same idea. Ever see anyone caught in a car wreck in the rain? Their day is screwed up, their car is dented, they're copying down some insurance information from a stranger AND getting wet. You can prevent them from getting more wet.
Tire gage - Not the crappy stick kind! Get a nice dial, with the extra button to let air out.
Travel car battery charger - I used to say "jumper cables" but then I met the travel car battery charger! You can jump start your own car with nobody's help. Truly a gift that keeps on giving and they charge your phone just in case. For the really ambitious, there are 2-in-1 charter/tire inflators.
Frisbee - Just in case a nice day breaks out and a picnic happens.
Milk crate full of books for little free libraries - just me? okay. Well I have too many dang books and hate finding a LFL that's not stocked up. If you're in a new part of town check http://littlelocator.org and map to the closest one.
Pair of scissors - so the drive through place doesn't mangle your coupons trying to rip them apart. A multi-tool or pocket knife with scissors is also an option.
Wine opener - Ever bring a bottle of wine to somebody's house for a party and they don't have a corkscrew? AHHHH! I have saved entire SWE meetings by having one in my glove box.
Survival blanket - okay this is maybe passable, but when I was flying airplanes it was a real thing in case you land in the tundra.
Gloves - be an organized person who stores gloves in their glove box. Not piles of old papers. I cleaned out my glove box and found insurance cards from six years ago. I decided to make a goal to store gloves in it, and only the necessary papers for registration and insurance. It can be done.
That concludes my list.