first of all, DON’T whisper- it strains ur vocal cords. just talk as you would normally if you have to, even if you have no voice.
Gargling with salt water if your throat is sore.
Drink something with honey and lemon, like tea. This one really works for me :).
Drink lots or suck on candies.
Refuah shleima and if this is a play, hatzlocha!