Singing

[Bart's Friend Milhouse]

Helium

EDIT: Actually you may want to try shouting at the top of your voice just to exercise it a little. Go somewhere like in the middle of the woods and just yell. I don't know if it will help but it won't cost a dime, it's not harming anybody else and it won't take too much of your time

Note to self: stop trying to be funny