There’s all sorts of advice about what to drink for your voice, and when to drink it. Here’s a little run-down:
Water: The vocal folds are mucus membranes, which love to be hydrated. Do consider the temperature of the water you drink during a performance. I find room-temperature to be more helpful in keeping my voice comfortable.
Tea: Brewed black-type teas are high in antioxidants that reduce inflammation, so that helps with a sore throat. Warm liquid is also soothing to irritated tissues.
Honey: Honey is full of nutrients, and combines well with the antioxidants in tea. Find honey made in your home area to help with allergies.
Lemon: It’s acidic, and therefore cuts phlegm. Not too much, though-remember these are mucus membranes. I put a little bit in a bottle of water for use during concerts.
Some folk are tea connoisseurs and insists on full-leaf tea for brewing. That’s great for a terrific cuppa, but grocery store packages teas are all right.
While there are lozenge-type products on the shelf with lemon and honey in them, I would recommend using actual fruit juice, and honey from a jar (organic, from local farmers is best).
AND the milk thing: drinking milk and eating dairy products produces thicker (not more) phlegm. However, phlegm is not a bad thing for vocal folds. The lower fat the product, the less phlegm produced. So unless you are sensitive to dairy products, milk before a show is fine.
And here’s some sites with good information: