Preheat oven to 250 degrees F (120 degrees C). Line baking sheets with parchment paper sprayed with cooking spray.
Beat the egg whites in a bowl with an electric mixer until they form stiff peaks. Gradually beat in the sugar, adding about 2 tablespoons at a time. Beat in the salt and vanilla extract until the mixture is glossy and holds its shape. Gently and lightly use a rubber spatula to fold the corn flakes, coconut, and walnuts into the meringue. Gently run the spatula through the center of the bowl, then around the sides of the bowl, repeating until fully incorporated. Drop the mixture by rounded tablespoons onto the prepared baking sheets.
Bake in the preheated oven until the cookies are very lightly browned and set, 20 to 30 minutes.
Let cool completely before removing with a metal spatula; warm cookies are very fragile.
