Test your repertoire first ( but briefly, so that you don;t use up too much voice!). My reactions to colds varies - sometimes I lose a note or two from the top of my range, so I drop keys a little if necessary (perversely I sometimes find my top notes come out better - explain that, someone, please!.) and sometimes certain word sounds suffer. After you've been at it a while I guess you get a feel for which songs will work with a cold and which to avoid. Funny ones are usually OK whatever. And as has been said before, whiskey works a treat (not if you have to drive yourself, though!) Lockets aren't too bad, either.