For long road trips back to NJ/NY, my usual 'car kit bag':
a qt of my fave oil, smallish jug of premixed coolant, tire gauge, lug wrench, Windex, paper towels, gloves, my bird dog, my fave home brew CDs, a cell phone I seldom use, and my golf stuff. Agree on the 'road service' card, I have through my car insurance policy. Sometimes I carry, if the states are reciprocal...
For non-road trip normal 'driving around': maybe the bird dog, and maybe a CD or two. And, occasionally carry then, too.
Even on a cross country trip I doubt I would carry more...I haven't needed too many tools and other supplies for my cars since the '60s and early '70s,
GL, mD