I learned this tip from a Maryland State Trooper. Keep a handcuff key in your glove pouch (if you keep in on the back of your belt) so you can reach it in a hurry if you end up handcuffed behind your back.
Also, it is thought to be bad luck by some, but I keep all my medical information and emergency contact information in Ziploc bag behind my trauma plate on my vest. The bag keeps the papers dry and clean from any water, blood, or other fluid.
The trauma carrier not only serves as a handy place to keep it, but also serves as additional motivation for me to wear my vest so that the medics and doctors have that information right away if I am unconscious.
Also remember to tell your patrol partners so they can find it.