1.) Coffee Maker
This is arguably the most important thing to have in your studio. No, it isn't directly music-related, but not everyone is a night owl like we are. Even if you don't drink coffee, every band appreciates a crappy caffeine kick in the face when your session reaches the 11pm mark and your drummer can't quite nail that fill.
2.) Box Of Random Percussion
No joke, a tambourine can instantly make a song not suck. There are very few arrangements which don't benefit from a shaker, maraca, or tambourine. Also, every song ever recorded needs more cowbell. In all seriousness, I've benefitted greatly from having this stuff lying around to give my artists more options to make their choruses pop.
3.) Box of Lost (and never found) Picks
Never buy another pick again. If I see a pick not in someone's fingers, it goes in this box. Every session I do is like getting a new shipment of forgotten guitar picks, I've got every thickness and brand you can imagine sitting here. It's like a "take-a-penny" jar at the gas station, one person pays in and another benefits.
4.) Drumstick Graveyard
This will save you and your session drummer at 12am on Saturday night when there is no music store open for a solid 36 hours. Sticks will break. Some will break less than others, those go here. It works just like the pick box, except most of the goods here are half-broken.
5.) Crappy Keyboard
For those of us not cool enough to have a baby grand sitting in their studio, this pawn shop star will suffice. There is nothing more useful to have sitting in a corner than the keyboard you took one month of lessons on in the 6th grade. It's great for picking out melodies or tuning a rogue string on the fly. Some even have MIDI functionality, which is useful to throw in that last minute piano line on the chorus.
6.) (possibly stolen) Music Stand
Remember these from the band hall in middle school? I've been using two of these I got in some sketchy trade for years. They're incredibly useful for vocalists and guitarists when they're tracking.
7.) 1/4in Guitar Cables Of Questionable Quality
Even if you don't own a guitar, you want these taking up space on your wall. Every guitarist will forget (or break) a cable when they show up. I'm a guitarist and I've been that guy more than once. I've collected these like picks over the years and I use them quite often. They're a lifesaver.
8.) Headphone Graveyard
Once again, I've collected these like picks over the years. I've got my solid go-to Sennheiser HD280s and fancy Shure in-ear monitors, but I've had to use these more than I like to admit. A band will decide to do gang vocals at 1am and you're dead in the water without a pile of these lying around. Don't throw away these poor, defenseless, mostly useless little soldiers!
9.) Mic Stand Boneyard
Most of these you're looking at barely work and are held together by duct tape. Why do I keep them? For the guy who shows up with a 15-piece 80's revival drum kit. It will happen to you, be ready.
I saved this one for last because it's no laughing matter. These are a MUST. I've had to redo more tracks due to an out-of-tune guitar than anything else. I've even made the mistake of recording an entire song to a guitar tuned by ear and I tried to tune vocals on top of it. Tune between every take. Tune too often. Pick up a Snark at your local music store for $20, it'll save you hours of work and senseless heartache.
Have anything else to add! Drop it in the comments below!