One of the useful things my mother (very proper and rarely drank) taught me when I left home was ‘you can always go in a pub’. I was always surprised that she did this herself when desperate. I was nervous the first time but she was right. If I don’t buy a drink (which would start the cycle off again!) I offer 50p change for any charity box on the bar. Some shops, even small ones, are obliging, especially for a child.
Re bus drivers on long routes, I once heard that they carry McDonald’s milkshake containers, oh dear!
My only loo is at the top of the stairs, I do tend to hover at the bottom, near the front door, if a driver I don't know asks to use it.