This is my first posting. I have got heaps from this site and hope that everyone keeps posting.
I have a class of 20 participants and for our warm up this week we have made a big circle on the floor. There are 4 balls of different shapes & weights (e.g. medicine ball, fitball, basketball) already positioned evenly spaced on the floor for the participants to make the circle around. The balls are passed around the circle - out in front, above the head & down below. Everyone is squatting at the same time as passing the balls. You reverse every so often too just to keep it interesting. We followed this with a few little powerwalks/jog around the gym floor. It went for about 5 minutes all up and it seemed to work well.
I hope you have fun with this.