For sitting with no support, I have to fold myself in odd ways to get stable (bend really far forward, legs almost straight, heals crossed). It is not a position for anyone with back or hip issues, that is for sure.Most definitely... I said it mostly tongue in cheek, although I was half hoping for some tips on body positioning with zero equipment. Where I live we have thousands of km of logging rd system that I can hunt off of. Many places I hunt are literally a 5-20 min walk off the rd, where I only bring in my binos and rifle. I've been trying to work on classic marksmanship but I have a herniated disc in my lower back and I find sitting and Kneeling hard positions to get into and be steady. My offhand sucks too.. but I'm working on it.
For the 5-20 minute walks, a set of trekking poles and a day pack might be enough to add significant stability without much weight. You could stuff a sleeping bag in the day pack to give it some light weight fill.
One of the Form Friday episodes of the Shoot2Hunt podcast covers things like using vegetation and such for support. The most helpful concept was that supports stabilize the shooter and the shooter stabilizes the rifle. It is a subtle change, but I can already tell that the change in conceptualization has made an improvement because I'm no longer focusing on how I stabilize the rifle, but on how I can stabilize my own body. Of course that is what you are doing by putting the pack under your knees, so you probably already have a better handle on this than I do.