Now here’s one that should be obvious, but that amazingly most gardeners don’t have in their toolkits. Anyone doing serious work in the garden needs some form of light magnification apparatus. Magnifying glasses are great, even with the risk of setting afire the item being examined, but they may not give enough detail. If the apparatus needs a table or desk to use it, especially if it needs to be plugged in, that makes using it in the garden a bit problematic. The obvious solution, then, is to go with a magnifier small enough to go into a pocket or bag, but with high enough magnification that you stand a chance of identifying that bug or that mold.
Thankfully, our friends at American Science & Surplus can help with this, too, with their choice of pocket microscopes. This one is a 30x pocket assembly, with the option of dropping in AAA batteries to use the lighted objective for further details. This one is a bit tetchy, because it practically has to touch the item being viewed to get good focus, but it comes in very handy in those odd circumstances.
I also have to mention that the ongoing improvements in laptop computers and tablets mean that we’re starting to see more processing power in the garden, and that means being able to do more than simply view items via a microscope. We also have the options of screen captures, cataloging, and identification via databases. Should I mention, then, the Digital Eyeball is tough enough to handle most garden environments?