I have read a lot of advice on different concoctons. Supposedly the best drink is Rooibos (Red Bush) tea. I have a problem with tannin and hate tea with a passion. I also know that alcohol relaxes muscles and then a bit is a good idea and more is bad. I want to be in control of my voice all through the night and a gig generally lasts 4 hours. My method is to drink lots of water during the day to stay hydrated and keep my chords wet. When I get to the gig I drink as much of a nice cold beer while I set up as I need. Then while singing I drink my own home made ginger beer that is only slightly colder than air temp. It is made from fresh ginger, lemon juice and rind, sugar and yeast. The ginger and lemon cut any flem that I might develop and the water rehydrates. The yeast makes it fizzy which makes it instantly refreshing. I purposly use less sugar than the recipe calls for. During breaks I drink beer (usually draught beer) again to relax my chords and prepare for the next set. I avoid any soda's, wine and hard tack as these all have a negative impact on my voice. Not cery scientific but it works for me and that is what counts.