Store leftover zucchini fritters in an airtight container in the fridge for up to 3-4 days. To freeze, let the fritters cool completely, put them in a single layer on a baking sheet lined with parchment paper, and place them in the freezer for a few hours until the fritters are frozen. Then, move the frozen fritters to a freezer bag. They will remain good for about 3 months.