Show the progression of long tones to moving up and down on the instrument. Also show the audience/parents how your class procedures work (rest position/playing position, toe tapping etc)
You can also feature each section playing their favorite line so far from the beginning book. Your section leaders can announce the lines and what they think is the best part of the semester. It gives the kids some ownership and it also fills time.
I've had to do this a few times and the parents and students like the extra attention.