Should your car ever wind up submerged in water a hammer could come in handy. Make sure it's a "break glass" type hammer, which has a point. Thick tempered glass is surprisingly strong.
The spring-loaded kind are a lot easier to use in a cramped car and by people with less upper body strength. However, those won't work on newer cars with dual-pane or laminated glass
Only the tesla truck claims to be bullet proof. This happened in a model y and the 5th person in the car narrowly survived because a bystander smashed the window.
Something pointed would be way better, doesn't even have to be big
Many are built into USB adapters for the old cigarette lighter style of plug, so if you've got a car with one of those plugs you can slot it in and if you ever need it you pop it out, put the plug to the window and slam, shatters right away, don't need that much force or space at all