Sour Mix
Most supermarkets will carry a bottled version of a Sour Mix, but just as a repuatable chef would rarely use bottled catsup in a recipe, so too you should avoid the temptation to use a bottled sour mix. In most cocktails that call for Sour Mix, you can instead simply use sugar (or Simple Syrup) and fresh Lemon Juice, or if you prefer, you can make your own fresh sour mix with the following recipe:

1 part lemon juice
1 part Simple Syrup