When you drink water on stage, it really helps you.
Drinking water can have a “reset” factor on the vocal folds. But H2O won’t actually reach the vocal cords themselves until the next day. Just another reason to try and stay as hydrated as possible.
Cough drops help your voice.
They can! But avoid any cough drops containing menthol (unless you are trying to suppress a cough) – which will dry you out. I use hard candies and cough drops not containing menthol to keep my throat moist.
Do not drink caffeine before singing.
Caffeine is just a naturally drying agent. A main component of coffee is actually water – this just continues with the hydration theme.
Whispering is a good idea when you are on vocal rest.
If you have “lost your voice,” I recommend speaking in a higher voice if you have to speak at all. Whispering can sometimes put more strain on the voice because it is putting strain on muscles you normally don’t use in that way.