Fortunately I'm less likely to need a hammer. My vehicle is one of the few with manual windows. I wear a knife I can get to in the extremely rare case the seatbelt jams. I took a course on how to escape a vehicle in water. They had a nice simulator.

In some ways it is better to simply roll down the window than trying to break it. Less dramatic and heroic but better. Break the window with the water higher on the outside and that water, and glass, is coming in rather quickly. The impact can be remarkably strong and it can easily wash you well away from your escape route. Tumbling and disorienting you when it does. Pop the windshield and you may end up head-down in the back seat. It also stirs up everything in the vehicle. Greatly increasing the odds of your getting entangled.

Mats, seat belts and all that gear and trash you have behind and under the seat can be expected to be floating around. Speed-hooks on boots, the knife holster on your belt and other things you wouldn't immediately expect can seem to reach out and grab stuff.

If you do pop a window be sure to hang on and brace for the oncoming flood.

A window being rolled down is, even if the water level is unequal, far less traumatic.