Conductor scramble: Start with the flutes. Have them line up to the side of the podium.
Each one directs the piece for a specified period of time, say a minute or two and the next student takes the baton a continues the piece with no break between conductors.
Movie music: Show an old silent movie. Let the kids make up a sound track as they watch the movie.
Music memory. Start a piece, and if you have no windows, turn the lights off ( no more than ten seconds) as they continue to play.
This happened to the HS Band (I think in 64) I was in at McFarland Auditorium as we were in the climax of POLKA AND FUGUE FROM SCHWANDA.
We didn't miss a beat.
Well, there's a few ideas. Let the kids come up with some new ways to get out of the rut.
There's a million ways to change the routine.