I have a list that is pages long of great ingredient substitutions, but I am just going to post the ones I use most often. This comes in quite handy in situations where you are out of something like buttermilk or catsup for a recipe.

Butter (1 cup)
* 7/8 to 1 cup hydrogenated fat plus ½ teaspoon salt
* 7/8 cup oil plus ½ teaspoon salt
* 7/8 cup lard plus ½ teaspoon salt
* 1 cup margarine
* 7/8 cup oil

Catsup for cooking (1 cup)
* 1 cup tomato sauce, ½ cup sugar and 2 tablespoons vinegar

Chocolate chips (1 ounce)
* 1 ounce semi-sweet cooking chocolate

Corn Syrup (1 cup)
* 1 cup sugar plus 1/4 cup liquid (use liquid that is called for in the recipe)
* 1 cup honey

Cream of tartar (½ teaspoon)
* 1 ½ teaspoon lemon juice or vinegar

Self-Rising Flour (1 cup)
* 1 cup minus 2 teaspoons all-purpose flour plus 1 ½ teaspoons baking powder and ½ teaspoon salt

Buttermilk (1 cup)
* 1 cup plain yogurt
* 1 cup minus 1 tablespoon sweet milk plus 1 tablespoon lemon juice or vinegar (allow to stand 5 to 10 minutes)
* 1 cup sweet milk and 1 3/4 teaspoons cream of tartar

Dry Mustard (1 teaspoon)
* 1 tablespoon prepared mustard
* ½ teaspoon mustard seeds

Shortening (1 cup)
* 1 cup minus 2 tablespoons lard
* 1-1/8 cups butter or margarine (decrease salt in recipe by ½ teaspoon)
Sour cream (I cup)
* 7/8 cup sour milk or buttermilk plus 1/3 cup butter or margarine
* Blend until smooth: 1/3 cup buttermilk, 1 tablespoon lemon juice and 1 cup cottage cheese
* 1-1/8 cups non-fat dry milk powder, 1/2 cup warm water, and 1 tablespoon
vinegar (let thicken in refrigerator)
* 1 cup plain yogurt (in cooking add a tablespoon of cornstarch to each cup to prevent separating)
* 3/4 cup milk, 3/4 teaspoon lemon juice and 1/3 cup butter or margarine
* 3/4 cup buttermilk plus ¼ cup oil
* 1 cup cottage cheese and 2 or 3 teaspoons of lemon juice, pureed in blender

Worcestershire (1 teaspoon)
* 1 teaspoon bottled steak sauce sauce

Plain Yogurt (1 cup)
* 1 cup buttermilk
* 1 cup cottage cheese blended until smooth
* 1 cup sour cream