Here are some ideas on what to do with old whey containers.
Top Idea:
Survival kit to keep in your car. Change of clothes, toothbrush, money, bars, flashlight, radio, etc. (via)
Honorable Mention:
I like to fill them up with sugar and return them angrily to the store, saying “I DIDNT BUY THIS SALT!” (via)
Use them for planting vegetables, yes i know its geeky ha