No one likes to be in the middle of a recipe and run out of an ingredient but in case this happens here are some substitutions.

Substitutions

Allspice 1 teaspoon - 1/2 teaspoon cinnamon plus 1/2 teaspoon ground cloves

Baking Powder 1 teaspoon - 1/3 tsp baking soda plus 1/2 tsp cream of tartar or

1/4 tsp baking soda plus 1/2 cup yogurt or buttermilk (decrease liquid in recipe by 1/2 cup)

Baking Soda 1/2 teaspoon - 2 teaspoons double-acting baking powder (must replace the acidic liquid in recipe with non-acidic liquid)

Bread Crumbs (Dry) 1 cup - 3 slices of bread, crumbled or 1 cups crushed cornflakes or 1 cup ground oats or 1 cup crushed potato chips

Butter 1 cup - 1 cup of regular margarine / vegetable shortening (baking) / 1 cup of oil (only if melted butter is called for)

Buttermilk 1 cup - 1 tablespoon of lemon juice or vinegar plus enough milk to make 1 cup. Let sit for 5 minutes or 1 cup plain or low fat yogurt or 1 cup sour cream

Carob Powder 1 tablespoon - 1 tablespoon coca powder, either natural or dutch-processed

Chocolate, Bittersweet or Semi-Sweet 1 ounce - 1/2 ounce unsweetened chocolate plus 1 tablespoon granulated white sugar

Chocolate, milk 1 ounce - 1 ounce bittersweet or semisweet plus 1 tablespoon granulated white sugar or 1 ounce sweet dark chocolate or 1 ounce white chocolate

Chocolate, unsweetened 1 ounce - 3 tablespoons natural cocoa powder plus 1 tablespoon unsalted butter, vegetable oil or shortening

Chocolate, white 1 ounce - 1 ounce milk chocolate or 1 ounce sweet dark chocolate

Citrus Zest 1 tablespoon - lemon, lime and orange can all be substituted for each other

Cocoa 1/4 cup - 1 ounce, square, of chocolate, decrease butter/oil in recipe by 1/2 tablespoon

Coffee, strong brewed 1 /4 cup - 2 tablespoons instant espresso powder dissolved in 3 tablespoons hot water

Condensed Milk 1 cup - Heat 1/3 cup of evaporated milk, 3/4 cup of sugar, and 2 tablespoons of butter until dissolved

Cornstarch (for thickening) 1 tablespoon - 2 tablespoons of flour, but you must cook for at least 3 minutes longer to thicken

Corn Syrup, Dark 1 cup - 3/4 cup light corn syrup plus 1/4 cup light molasses

Cream / Half and Half 1 cup - 7/8 cup of whole milk plus 1/2 tablespoon of butter or 3 tablespoons of oil plus enough milk for 1 cup or 1 cup evaporated milk

Cream, light whipping 1 cup - 3/4 cup whole milk plus 1/4 cup melted unsalted butter

Cream of Tarter 1/2 teaspoon - 1/2 teaspoon white vinegar or lemon juice

Egg 1 whole egg- 1/4 cup of egg beaters or 2 tablespoons of mayonnaise (baking only) or 2 large egg yolks plus 1 tablespoon water or 3-1/2 tablespoons egg substitute

Egg Yolks 2 large yolks - 1 large whole egg

Extract, pure vanilla 1 teaspoon - 1/2 of vanilla bean or 1/2-1 teaspoon other extract such as almond, lemon, orange etc.

Flour, all purpose 1 cup - 1/2 cup whole wheat flour plus 1/2 cup of all purpose flour (don’t substitute more than 1/2 the flour) or 1 cup self-rising flour (omit baking powder and salt from recipe)
The following substitutions require more leavening, so add 2-1/2 teaspoons of baking powder per cup of flour. Also recommended, use buttermilk and 1/2 teaspoon of baking soda instead of milk to decrease heaviness.
3/4 cup rice flour or 1-1/2 cups of oat flour or 1-1/4 rye flour or 5/8 cup potato starch flour or 1 cup rolled oats or 1 cup fine cornmeal

Flour, Bread 1 cup - 1 cup all purpose flour

Flour, Cake 1 cup - 3/4 cup all purpose flour plus 2 tablespoons cornstarch

Flour, Pastry 2 cups - 1-1/3 cup all purpose flour plus 2/3 cup cake flour

Flour, Rice 1 cup - Equal amounts of cake and pastry flour

Flour, Self-Rising 1 cup - 1 cup similar grade (all purpose) flour plus 1-1/2 teaspoons baking powder plus 1/4 teaspoon salt

Flour, Whole Wheat 1 cup - 7/8 cup all purpose flour plus 2 tablespoons wheat germ or 1 cup graham flour

Honey 1 cup - 3/4 cup maple syrup plus 1/2 cup granulated white sugar

Marshmallows 8 regular - 1 cup mini or 2.5 ounces marshmallow cream

Marzipan 2-1/2 cups - 2 cups almond paste plus 1 cup powdered sugar plus 2 tablespoons light corn syrup

Mascarpone Cheese 1 cup - 3/4 cup cream cheese beaten with 1/4 cup heavy whipping cream

Ricotta Cheese 1 cup - 1 cup cottage cheese

Sugar, powdered 1 cup - 3/4 cup granulated sugar

Sugar, white 1 cup - 1 cup of firmly packed brown sugar or 1-3/4 cups confectioner’s sugar (not for baking) or 3/4 cup maple syrup (reduce liquid in recipe by 3 tablespoons)

Sugar, brown 1 cup - 1 cup raw sugar or for light brown sugar sub 1/2 cup dark brown sugar plus 1/2 cup white granulated sugar

Sugar, Raw 1 cup - 1 cup light or dark brown sugar

Vinegar 1/4 cup - apple cider vinegar and white vinegar can be substituted for each other

Yeast, active dry 1 envelope (1/4 ounce) - 1 tablespoon active dry yeast or 1 tablespoon fast-rising active yeast

Yogurt, plain 1 cup - 1 cup sour cream or 1 cup buttermilk or 1 cup heavy whipping cream plus 1 tablespoon freshly squeezed lemon juice

If anyone knows of any that I have forgotten, please let me know and I will add them. Thanks Everyone.

Information from multiple sources: Joy of Baking information & photos from yummy nibbles & bits