Fisherman's Friend are okay for congestion but are NOT okay for sore throats. They are extremely harsh and contain capsicum which can irritate your vocal cords.
I do know a certain Cornish singing group that swears by Rum & Shrub.... but generally alcohol is a bad idea as well.

Ricola herbal drops or black currant gels are good, as is black currant herbal tea. I also use tonic water (with quinine) or candied ginger

Drink lots of water before you sing- hydrating is really important.

And relax & breathe- don't push your voice

Good luck

Julia