What measuring sizes do I actually need?

At minimum, you need: 1 cup, 1/2 cup, 1/3 cup, and 1/4 cup for dry measuring, plus 1 tablespoon, 1 teaspoon, 1/2 teaspoon, and 1/4 teaspoon for spoons. A 2 cup liquid measuring cup covers most liquid needs. If you bake frequently, adding 1/8 cup, 2/3 cup, 3/4 cup, and 1/8 teaspoon sizes will save you from constant double measuring.