It happens to us all at times. You forget to put something on the grocery list and then when you need it, panic.  Here are some substitutions that I have created and used: they work very well.

Ingredients substitution

Ingredient	Quantity	Substitute with
Allspice	1 teaspoon	1/2 teaspoon cinnamon and 1/2 teaspoon ground cloves
Anchovy Filets	2 whole	2 tablespoon anchovy paste
Apple pie spice	1 teaspoon	1/2 teaspoon cinnamon, 1/4 teaspoon nutmeg and 1/8 teaspoon cardamom
Arrowroot starch	1 teaspoon	1 tablespoon flour or 1 1/2 teaspoon cornstarch
Baking powder	1 teaspoon	1/4 teaspoon baking soda plus 5/8 teaspoon cream of tartar
Beau monde seasoning	1 tsp	1/4 teaspoon seasalt + 1/8 tsp garlic and onion powders and celery seed + 1/2 tsp seasoning salt, Process all in a spice grinder or coffee mill
Brown Sugar	1 cup, packed	1 cup granulated sugar plus 1/4 cup molasses
Chili sauce	1 cup	1 cup tomato sauce, 1/4 cup brown_sugar 2 tablespoons cider_vinegar,1/4 teaspoon cinnamon, dash of ground cloves and dash of allspice
Chives, finely chopped	2 tsp	2 tsp finely chopped green onion tops
Chocolate, semisweet	1 ounce	1 ounce unsweetened chocolate plus 4 tsp granulated_sugar
Chocolate, unsweetened	1 ounce square	3 tablespoons cocoa plus 1 Tbsp solid vegetable shortening
Cocoa	1/4 cup	1 ounce square baking chococlate and 1 Tbsp solid vegetable_shortening
Corn Syrup	1 cup	1 cup granulated_sugar plus 1/4 cup water. Boil together for 10 minutes. Cool before using
Cornstarch, (for thickening)	1 Tbsp	2 Tbsp all_purpose_flour Or 4 to 6 teaspoons quick-cooking tapioca
Ground Cinnamon	1 tsp	Cinnamon stick pulverized in a coffee mill or spice grinder
Heavy Cream, for cooking	1 cup	3/4 cup milk plus 1/3 cup butter
Light Cream, for cooking	1 cup	1 cup undiluted evaporated milk Or 14 tablespoons milk plus 3 Tbsps butter
Cracker crumbs, crushed	1 cup	3/4 cup dry plain breadcrumbs
Cream of tartar	1/2 teaspoon	1 1/2 teaspoon lemon juice or vinegar
Flour, cake	1 cup sifted	1 cup minus 2 tablespoons sifted all-purpose flour
Flour, pastry	1 cup	7/8 cup all-purpose flour
Flour, self-rising	1 cup	1 cup minus 2 teaspoons all-purpose flour plus 1 1/2 teaspoons baking powder and 1/8 teaspoon salt
Garlic	1 small clove,	1/8 teaspoon garlic powder or 1/4 Tsp instant minced garlic
Garlic salt	1 tsp	1/2 tsp granulated garlic and 1/2 tsp salt
Herbs, dried	1 tsp	1 Tbsp fresh minced herbs
Herbs, fresh	1 tablespoon,	1 teaspoon dried herbs
Honey	1 cup	1 1/4 cups sugar plus 1/4 cup liquid r 1 cup corn syrup
Ketchup	1 cup	1 cup tomato sauce, 1/2 cup sugar and 2 tablespoons vinegar (for use in cooking)
Lemon juice	1 tsp	1/2 teaspoon cider vinegar
Maple sugar	1/2 cup	1 cup maple syrup
Miniature Marshmallows	1 cup	10 large
Milk, buttermilk	1 cup	1 cup plain yogurt -Or- 3/4 cups milk and 1/4 cup sour cream
Milk, sour	1 cup	1 cup minus 1 tablespoon fluid milk plus 1 tablespoon lemon juice or vinegar (allow to stand 5 to 10 minutes)
Molasses	1 cup	1 cup dark Karo syrup
Onion	1 small	1 to 2 Tbsp minced onion or 1 teaspoon onion powder
Orange	1 medium	6 to 8 Tbsp orange juice
Parsley, dried	1 tsp	3 tsp fresh parsley, minced
Pumpkin pie spice	1 tsp	1/2 teaspoon cinnamon, 1/4 teaspoon ground cloves, 1 teaspoon ginger, 1/8 teaspoon allspice and 1/8 teaspoon nutmeg
Shortening,	1 cup	1 cup cooking oil (Only for recipes calling for melted shortening)
Sour Cream for cooking	1 cup	3 tablespoons butter plus 7/8 cup sour milk -Or-7/8 cup buttermilk plus 3 Tbsp butter
Sugar, powdered	1 cup	1 cup granulated sugar whirled in the blender until very fine.
Tapioca,  granular	1 Tbsp	2 Tbsp pearl tapioca 1 Tbsp all_purpose  flour
Tomato juice	1 cup	1/2 cup tomato sauce plus 1/2 cup water
Tomatoes, fresh	2 cups, chopped	one 16-ounce can diced tomatoes, drained
Tomato sauce	15-ounce can	6-ounce can tomato paste plus 1 cup water
Tomatoes, chopped 16-ounce can	3 fresh medium tomatoes	16-ounce can stewed tomatoes
Vanilla extract	1 tsp	1-inch vanilla bean split and scrapped
Vegetable oil	1 cup	1/4 cup vegetable oil and 3/4 cup applesauce or 3/4 cup applesauce and 1/4 cup melted shortening
Worcestershire sauce	1 tsp	1 tsp bottled steak sauce
Yogurt, plain	1 cup	1 cup cottage cheese blended until smooth or 1 cup buttermilk or 1 cup sour cream