hi Boo: I too advocate Sudafed as the least harmful medication to help clear up nasal drip/congestion problems, but also recommend drinking lots of water and/or sipping warm herbal tea with honey & lemon to help counter act the moisture loss effect to your throat & vocal chords by the Sudafed. Alcohol is particularly bad for a singer as it has a harsh effect on your throat & vocal cords stripping away moisture. One thing I find especially effective to soothe my throat is Slippery Elm. In addition to these things, the best singer's advice is getting plenty of rest before the gig.

Boo, looking forward to hearing how your gig went.

Scott