As Tjin said, your window breaking tool must be mounted in such a way that it will stay in place during a crash (an in this case possibly turning upside down). You must be able to reach it from your seat, find it in the dark and use it. Laying it in the console or dash means you will lose it in a crash.

In your scenario, you have crashed through a barrier, entered the water, it is cold, you are upside down, maybe injured. You may also be stunned or in shock, you may have others in the car with you. The initial crash has knocked the breath out of you. It is dark and you do not even know which way is up at first. The other people are flailing their arms and legs, if they are conscious, and you can't communicate with them.

That is what you are likely to have to deal with.