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 juices 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, If you need this, 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. It is easy to get a Doctor to give a prescription for an inhaler containing Albuterol. This dialates the Alveoli (Air Sacs) in the lungs to facilitate breathing. A non-prescription method is to take an empty over the counter inhaler and fill it with food grade hydrogen peroxide 3%. This works excellently.
