Get a banana hanger. It provides better airflow and keeps the ethylene gas that bananas emit from stagnating around them. This gas is what ripens the fruit so fast. In fact, you can put other fruits around bananas and they'll ripen faster as well.

The other benefit is that it helps prevent bruising on the bottom of the bananas and makes them last longer as well.

You can have bananas last for up to 2 weeks with this method.

Green. Green. Green. Green. Black.