The first thing that comes to mind is my siphon starter (the racking cane inside of a wine thief thingy).
At first I thought that it was gimmicky, but I love how easy it makes transfers. Not to mention sneaking samples of old mead.
Get one, it's worth every penny of the ~$12 it cost
Oh, and no homebrewery should be without a spray bottle full of star san. That's probably about as essential as it gets.