If you have leftover smoothie that you'd like to save, I recommend pouring it into a popsicle mold and keeping it stored in the freezer for an easy frozen treat. If you prefer to store the smoothie in the fridge, fill up an airtight container as close to the top as possible (to keep out excess oxygen) and store chilled for up to 48 hours. The smoothie will not have the same texture or flavor the next day, so just keep that in mind.