If watermelon's in season, this is our go-to for happy hour on hot summer days. This easy drink recipe is made with just 4 ingredients: watermelon, vodka, simple syrup, and lime juice. And the best part is, you can make a batch in advance, then store individual cocktail portions in zipper bags in the freezer. Then when you're ready for a refreshing drink, just stick a straw in the bag. Cheers!