Gray Card
Can be useful for setting white balance on site but I seldom bring
one along. Instead I do this in Adobe Lightroom. However, for very
exact color work in the studio a Gretag Macbeth "ColorChecker
Passport" system is what I use. In the field I seldom bring one
along. I sometimes do.
Focusing Rail
Many macro photographers prefer to stack photos working with a
focusing rail rather than turn the focus ring on the lens. Using the