This is from A Fork in the Trail's chapter on Recipe Creation. This bit appears on pages 26 and 27.
"You can purchase egg powder that is suitable for baking but not for use as scrambled eggs. If you have an allergy to eggs or you are vegan, you can purchase egg-free egg replacer at your local health food store.
If you prefer, you can make your own egg replacer. It is similar to egg whites and works well in white cakes, muffins, and cookies. The addition of oil mimics a whole egg in baking. To make the equivalent of one egg, mix 1 1/2 teaspoons tapioca starch, 1 1/2 teaspoons potato starch (sometimes found with the Kosher foods), and 1/8 teaspoon baking powder together and store it in a ziplock freezer bag. Then when you’re ready to use it at camp, add 1/4 cup of water and 1 teaspoon of vegetable oil. Beat the mixture with a fork until it becomes a little foamy.
Ground flax seed can be used in muffins, breads, or other baked goods, but it imparts a flavor that might be unpleasant in a cake or cookies. Keep the ground flax seed cool and away from air and light to prevent it from becoming rancid; this recipe is not suitable for use in hot weather or more than two days into a trip. Store the seeds in the refrigerator until you leave for your trip. To make the equivalent of one egg, use 2 tablespoons ground flax seed. If you cannot find ground flax seed, then grind whole flax seed. Pack the powder in a ziplock freezer bag, removing as much air as possible and storing it away from sources of heat and light. When you’re ready to use it, add 3 tablespoons of water to the ground flax seed and let it sit for 3 to 5 minutes. Add to your recipe like you would regular eggs."