Soy beverage powders are an excellent way to get 10-25 grams of soy protein in a serving. Look for defatted since it is lower in calories and works the same as the regular full-fat version for baking. It is better to experiment with smaller amounts. Soy flour will add moisture to mixes. Many bakeries include it in their mixes for this purpose.
Soy sauce is found with condiments or in the Asian food aisle.
Soy sauce is available in a lower salt version, usually called light or lite. Soy sauce does not contain a significant amount of isoflavones or soy protein to offer the health benefits of soy but does add a nice flavor to stir-fry dishes. Soybean oil is usually called vegetable oil or sold by brand name. It is found with other cooking oils. Soybean oil does not contain isoflavones or soy protein to offer the health benefits of soy but does work quite well for cooking, baking and dressing salads.