Alcohol

Elvis never drank alcohol.  Alcohol affects your ability to sing well.  You should not drink at all if you want to sing at a professional level and if you do, then definitely don’t drink on the day, or even the day before a performance.  If you did drink some alcohol, exercise it out of your system as soon as you can and drink a lot of water.

The Don’ts

Don’t drink alcohol, citric like oranges (acid reflux), milk (flehm), no chocolate, no hot sauce, no fizzy drinks like Coke or Pepsi.

The Yes

Warm water with a little lemon and honey to coat the throat.

Reduce Acid Reflux

Before a performance you can take an over-the-counter medication called Omeprazol.  It neutralizes any acid reflux you may have.

Water

Elvis can be seen drinking water at rehearsals and during his performances.  He knew about hydrating his vocal chords.

Inhaler

Right before going on stage Elvis would clear his lungs with an inhaler.  The proper solution to put in an inhaler is food grade hydrogen peroxide 3%.