Of the many egg substitutes available for baking, flax seed meal is among the most unlikely -- but among the most useful. Mix about 1 teaspoon of flax seed meal with 3 teaspoons of warm water per egg you wish to substitute. This method lends a slightly nutty flavor to the cookie, making it ideal for hearty recipes, such as oatmeal or chocolate chip. Buy heart-healthy flax seed meal that is already ground, or use a coffee or spice grinder to ground whole seeds yourself. Mix the meal with water until it takes on the consistency of egg whites.

Various oil mixtures replicate eggs in cookie batter, including the tried-and-true combo of 1 1/2 teaspoons of corn or vegetable oil, 1 1/2 teaspoons of warm water and 1 teaspoon of baking powder per egg replaced. Whisk the oil mixture until it takes on a foamy consistency. You may also use about 1/4 cup of vegetable oil as a substitute for recipes that call for just one egg. Avoid vegetable oil for recipes that call for more eggs, however, as you run the risk of an overly greasy cookie.

About 1/4 cup of unsweetened applesauce or mashed banana is a healthy, low-fat egg substitute for cookies and other baked goods. Fruits make for a smooth texture, but they also lend a mild fruit flavor to the cookie. You may use sweetened applesauce, but remember to reduce the amount of sugar in the recipe to offset the sweetness.

Store-bought egg replacers serve as all-purpose egg substitutes. Some vegetarian-friendly replacers contain soy and wheat, while gluten-, wheat- and dairy-free vegan replacers feature ingredients such as potato starch and tapioca flour. These substitutes aim to closely mimic the taste and texture of eggs in baked goods recipes, rather than add additional flavor. As each product varies, consult the manufacturer's label for portioning instructions and information about allergies and content. A 2-teaspoon mix of half unflavored gelatin and half warm water also serves as an egg substitute that won't greatly alter the taste of your cookie recipe. However, gelatin is not vegan-friendly, as it typically comes from animal collagen.