If I'm ever going to be leaving the house, I simply don't eat or drink anything until I get back. Public bathrooms are bad news, and I think working at a combination McDonald's/gas station when I was younger gave me a permanent fear of them.
I often do the same thing. I can't stand public restrooms, and it's only in the direst of emergencies that I will ever use one for #2(I"m talking about it's literally about to come out of my [censored], or I'm having stomach pains so bad I can't sit any more(Not even drive, if I can still sit, I make my wife drive). I'll take a piss in a public bathroom, always in stalls though, as I have issues with urinating in front of other people(when I went into the military, I had to be moved on from the piss test at processing and come back when noone else was in there so I could go).
My best friend is even worse then I am, it doesn't matter how bad he has to go, or how clean the restroom is, he will not, under any circumstances, go #2 in a public restroom. He will pull over and go into the woods and use leaves if absolutely necessary(I have been witness to this). Oddly enough, this comes from the guy who will happily catch fish, hunt all sorts of game animals, gut em, clean em, and then eat them with no problems whatsoever. I've asked him why he can touch a deer's [censored]sack but he can't sit on a public restroom toilet. LOL