I keep a small penlight handy in my shop. When I need additional light to drive a screw in a dark corner, I tape the penlight to my screwdriver. Flick on the light and the work area is illuminated! — Lane Olinghouse
This also works with a small keychain-size flashlight, and it helps to use tape that is easy to remove so you can switch it to whatever screwdriver you need for different projects. This hack is especially handy when working under the sink or inside other cabinets or for projects such as replacing a light fixture, which require you to cut the power when working.