I usually tell people to start with the most common and least glamorous threats first, and come up with solutions that generalize well, so that by the time they get to less likely but more flashy scenarios, they have nothing left to do to cover them.

Otherwise, you're going to have to deal with perpetual distractions and will end up with a mess of a preparedness plan. For example, if your darkest fear is that they will fire you for stealing paperclips, your "plan" may be to just come up with a really touching cover story for your theft. But then, what if they fire you because your ex cuts your tires and you're late for work? Perhaps run-flat tires can cover that! But what if they fire you because the Russians hack your computer and leak your e-mails about your stupid boss?...

I think the same goes here. Sure, situational awareness is important, but it should be on your radar long before you get to active shooters. If you visit CNN every day to learn what else you need to prepare for, you're probably doing it wrong.