They didn't mention using nettles (yeah, I know but they have poison ivy on the list).
Dock leaves - good for starting with.
The bit about washing is important. I've been on too many school camping trips where the kids simply don't wash hands, let alone anything else. A mate (ex Army, used to run major army campsites) showed the best way to set this up; a washing up bowl outside each toilet area, soap and shake-dry hands. Then nag people to wash hands.