My best advice to you is to serve and eat falafel as soon as it's cooked because that's when they are super crispy on the outside and warm and tender on the inside. However, if you have leftovers, simply store them in an airtight container and refrigerate for up to 2 days. Reheat them in a pan with just a little bit of vegetable oil. They will taste great, however, the texture won't be exactly the same.