A simple rotation of the sandbag (or kettlebell, if no sandbag is available) while descending into a reverse lunge will challenge your strength and core stability in the transverse plane.
When you add in the power of a swing, what you wind up with is a really cool explosive movement – the swing requires decelerating the implement at the bottom of the movement before you explode from the lead leg into hip and knee extension.
Eric describes how doing the YMCA song can help shoulder stability, why "your balls still suck," the right way to do a push-up, and how to do a DB Overhead Reverse Lunge.