Great thread.
My Grandfather (Father's side) spent his formative years on the Sioux reservation in the 1920s, but he never spoke much about it. His father aparently was a man who embraced the angry drunken stereotype so those years weren't a time I heard much about. I know he learned a lot from a favorite aunt and I wish he had been a more talkative man. He was a one meal a day man and thin as a rail. I had never put it together that a people with that lifestyle over the generations may have a genetic predisposition toward fasting. Darned good point.
Read "The Last Algonquin". One of the best books I've read. It tells the life of Joe Two Trees as he told it to a young boy that he met in the year before his death. Apropriately (to this thread) he mentions his way of bathing. He would find a creek or pond with some clean sand, wade in and scrub his skin with the sand. He probably had well exfoliated skin. He did this year round, as long as the ice was thin enough to break a bathing pool. He tells of his father aclimating him to cold water starting in his early childhood. No mention is made of his post bowel movement clean up process.
I can tell you that living in the Northeast as I do, wild grape leaves are my outdoor TP of choise. They can be found on the vine even long after the leaves die. They are broad, thick and soft enough. They come in handy.
Since having children I've taken to trying to always have a paper napkin or two close at hand and a roll of TP in a ziplock bag in the car. I seldom have to break that out but more than once I have. Tell you what, when with a group of people and someone (or their little one) needs it you sure look like The Hero when you hand over that roll.
TP is like duct tape, just have it around.
As a general outdoor or power outage/ water rationing bathing regime; I use the sponge bath. You can take a towel, bandanna or whatever you can get ahold of and do a respectable job of cleaning your body. You can do it with or without soap, but if you have soap be sure to get it all back off of you. Soap residue isn't good for you and a rash can become an infaction, which can become a serious medical issue. A wet towel wash by itself, preferably followed by fresh clothes can make a world of difference.
Clothes don't get spring fresh when washed in pondwater, but a good rinse and air dry is generally good enough. If you and your clothes get infested with lice, it's a whole different matter. I have no idea what to do with a lice infestation without the benefit of modern marvels such as Nix and a hot dryer.