1997 Acura CL, 84K miles:
The jack, lug wrench, and temporary spare tire that came with the car.
A few rags.
A sleeping bag.
A couple of bungee cords.
Small 12V plug-in work light.
1996 Subaru Legacy AWD wagon, 121K miles:
The jack, lug wrench, and temporary spare tire that came with the car.
A few rags/old towels.
A sleeping bag.
A couple of bungee cords.
Small 12V plug-in work light.
One quart 5W30 oil.
A tow strap.
I have a multi-tool that I switch from car to car. I take it with me on weekend trips, but don’t worry about it in normal local driving. This tool has never been used.
In winter I will carry extra clothing (coat, hat, gloves, boots). If there’s snow in the forecast I will carry a small shovel.
That’s what’s in the trunk, or the rear of the wagon. Each car also has a small flashlight in the glove box, along with at least one road map, an ice scraper on the floor behind the driver’s seat, and a collapsible umbrella in the door pocket.