Begin in a lunge position with one knee resting on the ground, holding a beach ball above your head. No ball? Hold a rolled-up towel or just extend the arms above you.
Straighten the front leg and step the back foot onto the cooler.
Stand on the cooler, raising your opposite knee into a 90-degree position before stepping back down into a lunge position.
Perform this exercise for 90 seconds on each side.