Megapro 15-in-1 screwdriver
The amazing Megapro 15-in-1 screwdriver was originally a gift to the Interop Team. I've since bought dozens for my students, and every toolkit I own has one in it. Just having a big variety of heavy-duty bits in the handle has been a lifesaver. For tiny screws, I use the iFixIT, but for rack screws and bigger, I use the Megapro.