GrooveTech Tools GTMLT1 Guitar/Bass Multi Tool

This is a great way to keep your Allen wrench and screwdrivers for your guitar together. The common sizes for nut, bridge, tremelo and truss rod are here. There are also a flat and a phillips head screwdriver. To top it off there is the adjustment tool for a Gibson-style truss rod.
This is almost the only tool you need. However I haven't seen a guitar that would require screwdriver heads this large. I think it would be better to have a micro-flat head screwdriver for things like saddle adjustment and the phillips head small enough to remove a scratch-plate. As it is the tools is really only useful for the Allen wrenches and you need find small screwdrivers elsewhere. Still the price is good and if you own multiple guitars you should find all the key sizes you need here.