Diet Coke is the one product that every bar should keep in stock, no matter what. Substitutes won’t do because nothing else approximates the chemical sweetness of Diet Coke itself, which is probably why the beverage doesn’t find its way into too many actual cocktails beyond a Jack and Diet. Balancing more complex flavors with every co-worker’s preferred afternoon pick-me-up is tricky, largely because Diet Coke was engineered to taste perfect on its own.