Every motorcyclist needs a good multimeter. Electrical issues can seem extremely complicated and very difficult to overcome, but they really aren't that bad once you have the right tools and can do the proper testing to identify the problem within the electrical circuit.
There are many fuel system cleaners out there, and a few of them are actually pretty good. One that I highly recommend is Sea Foam Motor Treatment. I use this stuff in everything - my lawn mower, my motorcycle, my car, my weed eater. Basically anything with a motor I'll dump some of this in there.
Every motorcyclist needs a good set of pliers for their toolbox and this set of five from Channellock is just about perfect. It has every thing you'd need to get things done.
Hex wrenches, or Allen wrenches as I always have called them, aren't needed for every bike, but if you need them and don't have them you're basically shit out of luck. You can get a set of these style wrenches from just about any retailer, but I'd suggest buying the Tekton long arm ball end hex key wrench set pictured above. (Note: All links are affiliate and when you click on them, and purchase something from Amazon you're helping support Wind Burned Eyes.)
Every motorcyclist needs good tools. One of the must haves is a good socket wrench set. The Stanley 69-piece socket set shown above is an excellent choice if you need a set or are looking to upgrade or add to the tools in your garage. All 69-pieces in the set meet or exceed ASIN standards for sockets and ratchets and feature a 6-point design. The black chrome finish keeps each piece from rusting over time.