Lateral strength with a touch of upper body

Clams are boring. Try these instead!
This combo targets the muscles that support our lateral stability whilst also encouraging good extended posture and upper weight bearing. My personal favourite is feeling the internal and external rotation of the femur in the hip socket.
When you go into your side plank, be sure to be on the blade edge of your foot (avoid allowing the ankle to roll).

No equipment, no worries, you can still get this one done.