Using a frozen banana leads to a creamier smoothie. Freeze it the night before or a few hours beforehand.
You can swap the peanut butter for any nut butter.
If you are using natural peanut butter, make sure you mix it before using.
To store: You can store the chocolate peanut butter smoothie for an extra day in the fridge but you'll have to give it a mix as the smoothie may separate in the fridge.
To freeze: Freeze the smoothie in an airtight container with some space on top as the smoothie will expand.