I don't get new stock in frequently enough to keep a dedicated QT tank up and running, but I keep on hand a 5g tank with its own pump, air lines and stone, heater, in tank filter, nets and bag of gravel that's ready to be set up at a moments notice and is broken down and bleached clean after each use. It's more commonly used for treatment than QT though, as I take in "rescue" fish fairly often.
Like most in the hobby, I've also got a couple totes full of misc. equipment, leftover substrate, hard scape pieces and nearly always have a few empty aquariums on hand. I tend towards smaller tanks (my largest just now is 37g) so my spares are proportional.
Last edited by Knotyoureality; 01-19-2014 at 10:51 PM.