Baking Powder: Use a combination of cream of tartar and baking soda. The ratio is typically 1:2 (for example, 1 tsp cream of tartar to 2 tsp baking soda). Note: there’s not a good substitute for baking soda if you need it for baking.
Buttermilk: Common substitutes for buttermilk include sour cream, plain yogurt, or a mixture of milk and lemon juice or white vinegar. If using a combination of milk and a “souring agent”, mix 1 cup milk (any fat content) with 1 tablespoon of lemon juice or vinegar (white or apple cider vinegar). Let it sit at room temperature until it thickens and curdles and resembles buttermilk.
Self-Rising Flour (got it’s own article here)
Flour for Farina (read about converting Italian style to US flour types)
Yeast: Active Dry yeast and Rapid-rise (Instant) yeast are interchangeable with two differences that must be considered:
1. Instant yeast is more potent than Active Dry yeast, so you’ll need to use less of it. As a general rule, you can use 2 1/4 teaspoons of Instant yeast to replace 1 package (2 1/4 teaspoons) of Active Dry yeast. Instant yeast also has a faster rise time when compared to Active Dry.
2. Active Dry yeast must be activated in warm water (110 F or 43 C) before it is added to the rest of the ingredients. The overall rise time of your dough will be longer than when compared to Instant.