>>29275210
Kicking (or hitting) the side-windows is probably the worst idea unless you happen to have steel toes AND very strong leg-muscles. Blunt force in general is ineffective. The outside water-pressure will in fact make it much harder in the same way it prevents you from opening the door.

Besides rolling down the windows early the best idea is to bash a bottom-corner of the window with a sharp and hard object. Cracking the windows somehow is really the only option.
Optimally a glass-breaking tool or screwdiver, else I'd try your sharpest and strongest keys.

Otherwise this >>29277377 would be my last resort though I'd probably be too panicked and stressed to even think about doing this as the car starts filling up.