Lie on your back and hold a cooler above your head. No cooler? Get creative and use something else like the water jug or your beach bag filled with towels (just be careful not to drop it on your face!).
Lower the cooler down to your torso and then press it back up.
Raise your legs up so your toes point toward the sky and your body forms a 90-degree angle.
Lower your legs back to the ground and then repeat, alternating between the cooler press and leg raise for 90 seconds.