This is an excellent question, and one that I don't think has any real answer. I have heard it suggested that lighter tools like the ResQMe, Benchmade Houdini or Raker Ring Tool could be affixed to the sun visor, although I think that's a bad idea if you have a heavier tool like the Vic Rescue Tool as there's a good possibility that it could become a projectile in an accident and do a lot more harm than good.
I've also heard that MOLLE type sheaths strapped to a seatbelt are a good idea, but be careful as the pressure of your body moving forward and the air bag moving back at you could cause damage. Maybe good if you want an imprint of a tool in your chest for the rest of your life, but maybe a tattoo might be a better option of that's the case.
Realistically I don't think there can be a specific answer as you can't account for all kinds of cars, all kinds of tools or any specific type of accident. I think the best idea may be to just have one in the glove compartment and one on your belt or in your pocket. Chances are if you can't reach either of those you aren't likely to be in a position to help yourself anyway.