This article should give you a couple ideas.
I like to combine them with other things like burpees, sled dragging, punching a heavy bag, etc.
One that I heard of that sounds tough, but have never tried:
Take your bag and pick it up and put it on a pedastal, the bed of a pick up truck or something, then grab it and put it back on the ground. Do a set number then switch sides. I think Poliquin wrote an article on this, possibly here in the archives.