This question popped into my mind at a professional exposition recently: is it polite to bring a drink into and out of a public restroom? It doesn't seem very sanitary somehow.
This certainly seems like the type of question that hasn't already been covered in a book of etiquette. If you ever do find a reference to this, please alert Etiquetteer.
Etiquetteer supposes it's one thing for a "bro" to bring a bottle of beer into a pub men's room, but quite another, at a big professional function like you describe, or a big public charity event, to tote a drink back and forth to the restroom. As a practical matter, where on earth might one put it while inside the restroom? Don't answer that! Etiquetteer doesn't even want to consider the options.
Good heavens, a glass of white wine could become the subject of Vulgar Speculation about a urine sample. A glass of red wine might involve a hazmat team after Vulgar Speculation about a urine sample!
No, Etiquetteer thinks it best to leave glassware and the drinks in them out of the restroom.