This is always a fun workout when you are with a group.
Form a circle. Every 30 seconds take turns calling out a favorite exercise. Repeat this for 20 minutes.
We did burpees, crunches, squats, jumping jacks, pushups, high knee raises, mountain climbers, plank, more burpees, and so on.
Constantly varied, almost random. Very easy to time with the Gymboss.
Run hard out there...