Warm up ahead of time. Do some comfortable scales, and stretch out the rest of your body while you're at it. Having tension in the rest of your body will only add to any tension you may have in your throat and chest.
Whatever you do, do *not* over sing your voice. Regardless of how acoustically unsound the environment may be, pushing yourself beyond your limits will neither be entertaining, nor will it be good for you (and it is possible that it can do permanent damage).
Sing to those who can hear you while projecting **comfortably**. Drink a lot, yes...but *NOT* alcohol. I am sorry, but that has to be some of the worst advice anyone could give you. Water with some lemon is wonderful. If you can stand the water to be warm, all the better.
And lastly, if you have any vocal training at all, now is the time to use it. Watch your posture, watch out for tension in your neck and face. Watch out for pushing from the upper chest and throat instead of from your diaphragm.
And relax. You're there to have fun. If you are relaxed, you are more likely not to push yourself, or have tense muscles (which causes you to strain all the more).