I typically hunt close enough to home, camp or boat that I don't bring anything along in a pack. However, I have on many occasions gone for several days with meager or, just as often, no rations. It is not impossible if you are conditioned to it. You really need hydration more than food and although food is essential for energy, the lack thereof is why we humans store fat. I have plenty of that. It can be uncomfortable but I have hunted pretty hard this way and none the worse for wear and tear. Of course this was in areas where I was well acquainted with the territory and able to call for assistance if neccessary. I would say it's not advisable for anything outside of those circumstances and would not work for those with medical conditions. In fact (before anyone gets cranky) it's probably not a good idea at all, OK! As I've said before, it takes conditioning yourself to it and I make that a practice.
Otherwise, I bring crackers, salmon or tuna, fruit, nuts, jerky and other easily packable foods.