I personally use honey, mildly mixed with warm water. A warm coffee also helps most times. If you have a sore throat, try cardamom. It soothes a sore throat. Even a warm salt water gargle helps if your throat is set.
The only thing you should drink before singing is water. Anything else might get stuck in your throat and make you not sing your best. For example, don't drink soda. It makes your mouth and throat kind of sticky. You should only drink water.