For no-holds-barred KD shooting, I use a leather rear sand bag filled w/ heavy zircon sand. Lookin' to upgrade to an Edgewood cordura/leather bag this year.
What I throw in my pack is a Redman Tactical
beanie bag - filled w/ poly beads and weighs about 1.5#. He also makes bigger sizes (aka the 'Tactical Pillow') that I've been considerin. A little heavier (3.5#) but more comfy for when you are on the gun for an extended period.
From time to time I've used a shooting glove inside a heavy shooting mitt... works like the aforementioned fist, only way better. I been accused of 'cheating' by some individuals over that one...