bird feeders out of milk jugs

Any creative idea of how to recycle a bottle half gallon of milk?

My son has a school project, they have to recycle half a jar gallon of milk. His examples were a bank, a bird feeder or a planter. I was hoping there was something more creative than we do …. Some idea?

The use for weights. I fill with water or gravel and use them to exercise at home. Great way to tone and weapons development, and cheaper than buying weights.