If you are planning a menu and your stores of a basic ingredient are depleted, you can often substitute an ingredient to produce relatively similar results. Substituting more than one or two ingredients, however, can substantially alter the outcome.
Butter/Margarine/Oil These are used to add fats to bind and moisturize ingredients or to provide fat for frying. These can be easily substituted for each other in the same quantities. Use some salad dressings if the flavors won't harm other flavors in the recipe. Many recipes are viable if you use one-third or one-half of the suggested fats.
Eggs When they are not the main ingredient, they are used to add moisture, to hold ingredients together, and to slightly leaven the mixture. To substitute for eggs used for moisture, add 2 Tbs of milk, water, or juice. To replace eggs used to hold ingredients together, add 1 Tbs of corn or potato starch and 1 Tbs of milk or water. You can also use 1/2 cup of applesauce of 1/4 cup of honey if their sweetness won't adversely affect the other flavors of the recipe. To replace eggs used for leavening, use 1 tsp baking powder or beat the mixture to add oxygen.
Flour We don't recommend baking with substitutes, but in cooking flour can be replaced. Use cornmeal, semolina breakfast cereal, well crush bread or cracker crumbs, crushed corn flakes or similar breakfast cereal, or rice, couscous, or pasta powder made by crushing and grinding dry rice, couscous, or small pasta. The results will be slightly more grainy that when using flour.
Leavening Agents In place of baking powder use 1/3 the amount of baking soda. In place of baking soda use 3 times the amount of baking powder. You can substitute 2 eggs or reconstituted egg power for baking soda or baking power, but you need to reduce other liquids slightly to compensate for their moisture. Nothing adequately replaces yeast in breads or cakes, but for some other uses you can substitute baking powder or baking soda.
Milk Milk is used to add moisture to recipes. Replace it with reconstituted evaporated or powered milk or water. If you are making a dessert you can use coco mix. Otherwise you can use a milky substitute made from mashed oats or rice and water (Strain before using) or coconut milk if the sweetness won't overwhelm other flavors.
Sugar Because they are primarily used to provide sweetness you can substitute honey, syrups, jams/jellys, fruit juices, or applesauce.