A great use for shirts that you no longer need: Recycle them into garden ties.
Cut the sleeves off. Then start at the bottom and cut the hem off. Then cut a strip about 3/4 - 1 inch wide (depending on how thick the T-shirt is) all the way around, angling it a bit wider as you near your starting point. Continue to cut spiral strips until you can cut no longer.
Stretch the strips and roll into a ball the way you'd roll a ball of yarn.