Milk? Warm milk? And, drink a wee bit too (I prefer skim milk for drinking). The muscles need the calcium to be able to respond to flexing. It's all about the negative and positive charges in the sarcoplasmic reticulum and the mitochondria. If I drink a glass of skim milk twenty minutes before playin Hran, I can do much better for longer... I assume this would be the same for guitar... and, why not for singing, as well?

As for a gargle, I just "think" that milk with some fat content would help grease the skids.... no... ??? Just a thought.