OCTAVER!!
Now, not a certain brand/model/etc, but I don't know how I lived without an octaver.
I keep the output of the clean-octave and the octave-below perfectly even, and I keep the output of the pedal itself perfectly even with my dry signal, so it's never a "boost" situation when I engage the pedal, only an octave situation. I use it so often it's not even funny.
My current octaver of choice is the Aguilar Octamizer. I like it ok, it's certainly a vast improvement from my first octaver (that was a crappy Beringer)! But I may still hit eBay for an old OC-2 at some point. (And of course there's the grail- Ashdown makes a Pino Palladino sig octaver that I HAVE to try someday!)
My board right now also consists of a Way Huge Pork Loin overdrive, a Mooer Sweeper envelope filter, a Boss orange Distortion (left unplugged unless I'm going to use it for the song, she's noisy!), a BBE Sonic Stomp (I don't go through an amp, I go direct live, so this is a close second for my most indispensable pedal!) and a Snark chromatic tuner/mute switch. I have come to love and regularly use all of these, although I'm always searching, expanding/consolidating, etc...
BUT I'll never play without an octaver by my feet
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