You can freeze peeled bananas by slicing them into 1/2-inch pieces and placing them in a Ziploc bag. They will stick together so you have the option to put one sliced banana per bag so you know exactly how many frozen bananas you have. I prefer to freeze bananas unpeeled and whole. I simply place them in a Ziploc bag and freeze. When I need to use them, I bring how many pieces I need down to the fridge to thaw overnight. Note that frozen whole bananas tend to release lots of moisture once peeled so you may want to remove some of the excess liquid before using.