From context, Deitsch (the speaker) is talking about practices related to school shootings. The town hall is being held in Florida, where "code red" seems to be a standard term for an immediate threat to students and staff. "Drills" in this context would refer to a scheduled practice for a code red situation, and of course an active shooter is a specific, real code red scenario.
This is a good example of the rule of three in rhetoric: Deitsch is using three closely linked examples of what modern students are facing today in ascending order of seriousness (preparing for threats, real threats of any kind, real threat of a school shooter). Using three specific examples instead of a more vague umbrella term drives home the idea of these things being pervasive in his life and the lives of others.