Emergency trauma kits are more important than a firearm. In my experience they are far more likely to actually be used. I've been on the scene of three vehicle accidents with trauma victims and in one case the EMT's were 45 minutes away.
I've come to prefer a tourniquet and stop the bleed kit over an extra magazine and heavier pistol.
For those of you not already EMT's or emergency trauma doctors, there is a free, online Emergency Trauma Course that I thought was fantastic.
“Emergency Trauma Response” (ETR) is a comprehensive training program for anyone interested in being better prepared to deal with massive trauma. Building off the popular “Stop The Bleed” program, ETR