I have a heavy serrated folder with the glass breaker tip protruding from the handle's end always at hand in the car, clipped to the DIY cutout in the side of the belt's well (along the car's side beam) and also attached to it with a short lanyard. That piece of the frame seems to have an equal chance of surviving in the crash as myself. I don't like the slot like mini cutters, as for example, under the water your vision will be quite inadequate for using it on the belt, especially under the stress. A knife like tool is the way to go here, IMO, as you have much more experience using such a tool.