We use citrus juice and zest in lots of ways. If a recipe calls for just juice, we zest it first. If we think we're going to use the zest in a day or so it goes into a snack-sized zip-top bag and into the refrigerator; if we don't have a use for it in mind, the bag gets labeled and tossed into the freezer.
If the recipe calls for just zest, we go ahead and juice it after zesting. Freeze the juice a tablespoon at a time in a standard ice cube tray.
Zested and juiced lemon and lime halves can be frozen in zip-top bags and used later to flavor dishes, or to go into a bowl of water to prevent apples, potatoes, and artichokes from browning after they've been cut.