In addition to the excellent advice already given, I'll add that it's important to a) stay on top of incoming, even in the midst of crisis (i.e., empty your inboxes daily), and b) continue to review your actions list even while in crisis mode. It's easy to focus entirely on the "as it shows up" work, but the other work is still important (or it wouldn't be on your list), and that stuff can blow up without attention. Finally, it's good to re-evaluate how much of your time is spent in reaction mode. Maybe there are changes that need to happen (via you or your boss) to reduce this.