I've got a few of M2-M5 taps but I've been meaning to buy a whole tap and die kit. Its on my listI think pretty much everything has been mentioned here. But an uncommon item I have are metric form taps of various sizes. Form taps are great for RC when you have a threaded hold that has been buggered up. Form taps don't cut material away. They push material or "form" it into a thread. The create a much stronger thread.