Give the speech where you say: “Finish strong. It may be the 6th show for you, but it’s the first time these people have seen the show. Give them a show to remember.” Recognize all the people behind the scenes. Recognize the kids who are graduating or leaving after this year. Work hard to impress on them the dignity and importance of this last performance. When kids are invested, you get better performances. It’s like anything, when you take pride in your work, the work gets better.
Some schools have an awards ceremony of sorts after the final show. Usually the kids organize those awards. An adult should supervise the awards; kids can be cruel. If there’s a cast party, it should be well supervised also, as exhausted as everyone might be, you don’t want to deal with the fallout from an out of control cast-party.