Here are a few exercises to help keep your workouts humming along. The Man Maker lives up to its name. Try it with 25-30 lbs in your PKB, or bump it up to 40lb but remember: 40lbs of sand tends to feel more like 55lbs of iron.
I love that you can do a whole lot of medicine ball exercises with the PKB. Some of my favorites involve abdominal workouts. And my favorite is the Overhead Sit-up. Try it with a 20 to 30lb in your PKB. You'll thank me later ; )