How do you change up lesson plans when an unforeseen circumstance happens during the day?

"At the last school I worked at, unforeseen circumstances happened every so often. The administration really did a good job making our lives easier and limited these occurrences. But, when this did happen, I needed to go with the punches. Flexibility is the biggest part of the profession I believe. So, I would limit an activity or move it to the next class period to make things work out for the better."