My Cruz tools 3/8 inch Powerdrive t-handle fits nicely under the rear seat for easy access to many of the bits and sockets I'll need for work on the bike. It's missing 18 and 19 mm sockets which are needed for wheel removal. I stuck a neodymium magnet to the side of it that I can stick to the tip in case I lose a piece of metal in a hard-to-reach part of the bike.
It has to be positioned in this exact placement or else it gets in the way when I reinstall the seat; I may rig up a retaining piece to dampen vibrations and make it easier to get it in just the right configuration.
http://www.amazon.com/CruzTOOLS-TSDS.../dp/B000GTYPQA