Other than the guitar and amplifier, what other gear(effects, strings, accessories, microphones, recording equipment, computer programs, etc...) do you think is absolutely essential to what you do as a musician???

For example, If I want distortion, I just have to have the rat distortion pedal. I just like the way that thing sounds. Or if I am going to mic my amplifier, I want to use a Shure SM57 mic because those mics really pick up the full spectrum of sound.