Too much force, too many repetitions, and too much force or volume can all result in injury. Musicians tend to be stuck in one position and repetitive strain injuries can occur. Diet is obviously critical to maintaining optimal health. Many 24 hour supermarkets stock easy to prepare frozen foods that can be heated up in the nightclub's microwave. Try to keep caffeine and alcohol to an acceptable minimum- having two beers and not four.
Smoking is obviously a no-no.
Anybody working in a bar is getting way more smoke than their personal limit of second hand smoke, to begin with. Smoking tends to dry out your vocal chords and limits your singing range. Other than Rod Stewart, I can't think of any other successful singer who can sing with damaged vocal chords. I am a singer. The muscles in the throat are so delicate, they are like onion skins.