I second everything Phillip wrote. DON'T use any lozenges or sprays that will numb your throat or are so strong that they can affect your vocal cords. Save the Fisherman's Friend and other strong lozenges for when you have a cold or flu. DON't use them before a performance or as a singing aid. Keep with what Phillip recommended - plain water, no acids in it (like fruit or vinegar) and don't eat a big meal before you go on. Start warming up your voice before the performance. Begin by singing in the shower, then keep gently singing scales from the bottom of your range to the top of your range while you are driving to the gig. When you are there, get a glass of water to have nearby for sipping when you feel dry. Wait to drink anything stronger for AFTER your performance.

Check out the mega-thread I collected called "Threads on the singing voice". Lots of info there.

Have Fun.

Alice