We've stocked up on TP -- low-grade, not soft, emergency TP. We can fit a case of 198 rolls in an old USPS canvas mail bag; each one is in a
ziplock, because, hey, the bags will have a purpose also, if we ever need to use the emergency TP.
In a real, ongoing SHTF, those two cases will eventually run out (no pun intended). When I was a kid, cattails were a decent emergency wipe. Here
where we live, near the sea, I can imagine digging a latrine, then doing a "rinse" in the ocean. While seawater can carry human pathogens, mostly
it is good for treating bodily injuries, so I can see how that 'morning rinse' might become habit.
My vagabond relatives in the old west carried a "wash rag" or three. They were used for wiping, and ONLY wiping, and cleaned wheneven they came
across running water. This, of course, presents a danger to those downstream, so in a regional SHTF, it would be prudent to also have a washing
vessel to take water from a stream, lake or river and wash the rags in.
Other things used in my past (hey, you asked!!!) Some kinds of bark, such as cedar can be rolled and abraided into a serviceable TP. Coconut
husks are easily roughed up into a useable wipe. Almost any piece of uncontaminated cloth. Corn silk.
For me, it isn't really an issue in a SHTF. Much more of a pressing concern to a man my age is underwear. I can fabricate a shirt or pants from
home-tanned hide or cloth, but underwear
......... ain't much of a substitute for that.