Or, you could just collect half cents. They were so limited in mintage that even the "commons" feel like keys...
Each time I start a new series, I look at the overall mintages, trends, condition rarities, and etc, when assigning what I believe will be the keys, to the set, which is why when doing barber dimes, the 1895 o, and the 1901 s made it near the top of the list but the 1909 D and the 1915 S came in as commons or just better dates, even though they have low mintages, there are enough of them around and they are new enough, that its not going to break your bank to get one, on the other hand the 1913 S starts to be a major condition rarity in grades above fine, which moved it up on the list. It all depends how you are focused on a particular series, and what type of set you want to build