What are they?  The dustpan and broom.

Yes, I said it.  These two tools are the most important tools we can have on any job-site.  They are even more important than an electrician's pliers, or even a voltage meter to make sure something's dead before we work on it.

The first thing a customer notices when they walk into their home or office after a contractor has been doing a project of any size, is the cleanliness of that space.  It doesn't matter if a new light fixture is installed exactly the way it should be - if it's illuminating a messy floor, then it doesn't matter how good the actual job was performed.

"It's like they were never here!"

It's always great to hear this statement from a customer after we complete a project, whatever its size.