Here in the UK we have a special road tax for cars, and we were given a tax disc which we had to stick to the wind-shield so that police could visually check that the tax had been paid for any vehicle they encountered. Now the police have bought a computer, and as of last October we don't need to show the tax disc any more. Hence:

Replace your tax disc with an Emergency Contact Disc to provide vital information for first responders at medical emergencies or road traffic collisions.

More details here. The idea is that stuck to the wind-shield it will be easier to access than something in your wallet. The disc is folded so that specific information is hidden; you need to get into the car and retrieve the disc to see anything confidential.

I'm not entirely sure it's worth doing, but if it is then it's also worth doing outside of the UK.