During a conversation with a family member who grew up on a farm in Europe, I learned that when they were outdoors and no paper available,
Dock Leaf was commonly used in its place. It is a common weed that also has disinfection properties and has been used for treatment of hemorrhoids. (A natural medicated toilet paper).
Note that another plant, Stinging Nettle is often found growing nest to Dock Leaf and would not be a good choice.
Dr. Howard Hindin