I don't stock parts at all, with a few exceptions:
a. 0.1uF, 1uF, 2.2uF, 10uF, 33uF MLCC capacitors for obvious reason -- I will use them in almost all projects.
b. Reference grade parts such as rubidium clocks, OCXOs, I stock them as lab or equipment references.
c. Excessive parts from previous projects.
d. Big boys such as ultracapacitors, batteries, display modules and etc.
e. Boards and kits used from previous projects.
Besides, I stock no parts. The reason behind this is simple - I do SMT designs all the time, so anyway I need to wait OSHPark to deliver my PCB, and in the meantime, I have more than enough time to order things from DigiKey.