Okay, I'll chime in.
Drill bits: sooner or later you find you use maybe 10 sizes for 90% of the work. Buy them in packs of 10.
Buy GOOD measuring tools! Always! Starrett or Mitoyo or something comparable. You're in a technical field where 0.001" can cause injury to you or your customer, you cannot afford to have tools that cannot measure reliably to this standard. The best tools in the world will still make **** if the measurement's wrong.
Screwdrivers: Forget the Chapman. Buy the Brownells. You can always add more bits, and you can buy extras to grind to the sizes you need. Then go out and buy 3-4 dozen Craftsman (or similar) and grind the bits to the sizes you need. If you can't grind a screwdriver you're in the wrong business. Every good gunsmith I know (a fair number) makes his own turnscrews. You want to get ones with a square shaft so you can add torque if you need to. You need both solid and replacable bits. (Note: I find that I prefer all my handles to be the same size (a point I've made to Grace multiple times). Find a size that works for you and try to stay with it.)
Make your own punches. Steel, brass, copper, nylon, etc.
Files: You need to learn files. Other than screwdrivers files are your most used tools. You'll need 50-100.
You really need to find an industrial supplier (MSC, Garrett, etc) and quit trying to get what you need at Lowes. Get your stones and cutting tools at the same place. You also want to find somebody locally who'll sharpen and customize your cutters.