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.
Go to any gym these days and you see most trainees doing an endless number of reps all in the hopes of attaining the oh-so elusive and fleetingly short pump.