I have a "crash kit" in my motorcycle tailbag. It has a plastic bag and tape to cover a sucking chest wound, surgical tubing to tie off limbs with punctured arteries, and a coagulant powder to stop major bleeding. The basic scenario is to make sure their airway is clear and stop any major bleeding in hope they won't expire while I ride off for more competent help.
There are some other items in the crash kit - three chemical light sticks and a Mylar "space blanket" - for marking the crash site, since the areas we used to ride were winding mountain roads with no cellular service. Finding the site again, particularly in the dark or in the rain, could be a big problem. The whole package replaced one of the water bottles I carried in the tailbag. You wouldn't need anything like that for a gunshot kit.
Some people find the selection odd. My scenario was basically to be able to stop someone from bleeding out while I left them to go find help, which might take a while, and to be able to find them again later. I wound up being first on the scene at serious crashes *twice* on the same day back in 2006, which is what prompted me to put the kit together.
There are still vast areas where there ain't no freakin' cellular service, and you have to go beat on someone's door and ask them to make a call on their land line... if they have one.