There's a great tea called Throat Coat and it's available at many grocerie stores. It's great if you have a sore throat the day of a performance.
I was recently in a show and i had a very dry and somewhat sore throat from sleeping with my window open the night before, so I had a thermos of hot water that I had let cool for a bit so that it was warmer than room temperature but not piping hot. It worked really well. Cold water seems to make me more thirsty, especially if I haven't drank anything for a while.
It's better to take small sips of water ocassionaly to be constantly hydrated rather than chugging your waterbottle before you make your entrance.
Dairy doesn't seem like a good thing. Whenever I have mucus I end up trying to swallow too much on stage and it makes me look nervous.
-Was that a fart?
-My fault, I fear.