I used to carry a ton of tools in previous cars. Extra fuel pump, alternator, wiring, and a boatload of tools. As I get older, I carry less stuff. Now in the 32 roadster, all I carry is what will fit under the glide seat. No spare parts anymore. I found out whatever goes wrong with the car- it's won't be the part I'm carrying. So- it's one of those wind up LED flashlights (no batteries to sweat), end wrench set, socket set, allen set, 6 way screwdriver, canvas D ring axle tie downs (flatbed tow likes to use chains & hooks) & my cell phone. I installed a 12v cig outlet under my seat to charge the cell phone on the road.
And most important- MY AAA card!