I have dedicated on of my smaller storage compartments. Jumper cables, small air compressor, motor oil, WD40, Windex, tool box stocked with variety of tools, electrical and duct tape, fuses, box knives, VOM meter, spare light bulbs, 12v circuit tester. And leave room for more stuff as you think about them.
A hammer! especially when loaded. very quick and easy way to find a soft tire! listen when you hit them if they all sound about the same they are about the same pressure. if one sounds different check the pressure, might save yourself hassle of having a blow out. I check mine after every few hours of driving.