I started my stock based on what was cheap and available, resistors of common values. looking for cheap Capacitor and Resistor starter kits with multiple values is a good start, anything else you can add as needed.
I also got a good deal on 74hc595's and MAX7219 along with several LED/LCD displays and some 3904/6 transistors!
Anything else I add as needed as this serves as a good base for most things!