We do and we don't. Most of our emergency stuff is also used in camping. However my goal is to have a emergency kit for each car and the house, just in case. I have done one in the past, and it is quite difficult to pack everything in one container. I have put in a change of clothing, thin but warm blankets, first aid kit, torches, and food.
My emergency kit was purchased already assembled as a large first aid kit which is kept in our car. It's the size of a small laptop bag and has all the essentials including an emergency blanket, a swiss army knife and obviously First Aid materials like gauze. Everything is labelled and packaged in clear plastic pouches inside the kit, so is organized and easy to find.
I always feel better about taking road trips knowing that if something were to happen, I am as prepared as I can be. My wife and I do a lot of trips through the Rocky Mountains and there is no cell service for a large portion of the drive. If the car were to break down or we got into an accident, we could be on our own for quite a while.