During the Civil War, the Union Troops in the field lived for weeks on end on salt pork and hard tack. The Confederate troops on far less. So far as I know, actual starvation was not a big problem.
I think that once you stop eating lots of food, your body metabolism shifts, and you start burning fewer calories. You are hungry, and you feel weak, but hundreds of thousand of years of evolution have molded us so that we can go through periods of near starvation without dying.
And, from the things I have read, after about two weeks of having little food, you stop being really hungry. Your stomach shrinks, your body conserves calories, and you lose your appetite.
I would also imagine that as little as two thousand years ago, and just 200 years ago for the Indians, it was very very common for people to go three or four days without eating, just like wolves and other big predators. When you killed something, you gorged on it, slept a few days, and then started hunting again.
In short, these people who were out on the plains in possees and tepees a couple hundred years ago just weren't suffering like we would today. They were use to it.
And, just 75 years ago, about 50% of all men in the U.S. were malnourished due to lack of food from the Great Depression. I read somewhere that when WWII started, about half the men drafted were in extremely poor physical condition due to lack of food, very poor shape.
My father lived in abject poverty during the depression, and he lived on one bowl of oatmeal and one bowl of navy beans throughout most of the 1930s. When he was 18 years old, he weight 85 pounds. About once a week, his mother would bring home a piece of three day old flank steak from the butcher, put it on the wooden floor boards, pound it for five minutes with the back of a claw hammer, and cook it up in a "stew" with just flour added in. Those foods, plus the bags of potato peelings he would scrape out of the garbage cans behind the restaurants in downtown Richmond, kept them alive.
When he was about 16, he and his little sister got in a fight over who would get to eat the last egg she was scrambling, and she stabbed him in the stomach with a two-pronged meat fork. Luckily, it didn't penetrate his gut sack or he would have died of peritonitis. He is 91 now, and will show anyone who asks his scar.
So, compared to people who lived through the Great Depression, most of those posse guys probably ate pretty good.