Which ingredient is part of the Tom Collins recipe?

The Tom Collins is a classic cocktail that typically consists of gin, lemon juice, simple syrup, and soda water. The key ingredient that fits well in this context is the sweet and sour mix. Sweet and sour mix provides the necessary balance of acidity and sweetness, mimicking the combination of fresh lemon juice and simple syrup traditionally used in the recipe. This inclusion not only enhances the flavor profile of the cocktail but also makes it easier to prepare, particularly in a bartending environment.

The other ingredients listed, such as cranberry juice, peach schnapps, and grenadine, do not align with the traditional composition of a Tom Collins. Cranberry juice is more commonly associated with drinks like the Cape Codder, peach schnapps is typically found in cocktails with a fruity emphasis, and grenadine adds sweetness and color to drinks like the Tequila Sunrise but does not belong in a Tom Collins. Therefore, sweet and sour mix is the most appropriate choice in this context.