I still have a 40 pound tool box in the trunk, and jumper cables but for years I also had a 12v impact wrench , a hydraulic jack, and a bag with a change of clothes.
ON and off I carried a jug of gasoline, but still have power steering fluid, brake fluid and windshield washer fluid.
After a learning lesson, in a newly purchased car i would take a new water pump, alternator and fan belt.
Have not taken a long trip in years now alone , so I am getting lax.