Adding to the other great answers- a multitool, a bigger one if you can allow it for example when travelling by car, a small one or even knife-less like the Lea

Adding to the other great answers- a multitool, a bigger one if you can allow it for example when travelling by car, a small one or even knife-less like the Leatherman PS if you fly. My tiny Victorinox Classic saved so many times- cut nails, loose wires or fibers, fix glasses, fix broken zippers, treat small wounds and splinter etc.