Run, Hide, Fight
It is unlikely that most people will get caught up in a mass shooting incident, but situational awareness can be vital and should become a habitual form of discipline. There is a rule for fighting fires that says "never let the fire get between you and the exit." That's good advice for avoiding any kind of potential threat.
A precept for your handling of emergencies says that "you won't rise to the occasion, you'll fall to your level of training."
What is your level of training?
-fl