In a way the messed up evacuation was to your advantage. We learned that on 9/11 when my wifes work evacuated the lawyers before the staff and a couple other people have mentioned similar stories to me, that those in charge of the evacuations are not always looking out for you, sometimes they have to look out for 'more important people' first. So you were able get out ahead of the crowd puts you at an advantage.
I'd try to add a little to your EDC so if your away from your desk and can't get to your gear your still prepared. A handkerchief in your pocket won't look out of place but could cover your nose and mouth to prevent breathing in too much dust for example.