What's the one tool you never service a unit without?

A universal door bypass tool is the one tool I never service a unit without. It is a small, flat piece of metal with notches cut into it that can slip between the door and the frame to lift the latch from the outside. I learned this the hard way when I had to drive back to the shop for a crowbar after a standard unit's latch jammed shut on a construction site. Now I keep one in my pocket at all times.

Beyond that, I always carry a multi-bit screwdriver for latch adjustments, a small bottle of penetrating oil for rusted hinges, and a full set of replacement parts: latches, toilet paper holders, and deodorizer blocks. For events with deluxe units or restroom trailers, I pack extra paper towels and soap cartridges because guests notice when those run out. The service frequency depends on use: weekly is standard, but a festival with heavy traffic might need mid-event servicing, and a flushing unit in summer heat will need more frequent pumping to avoid odors. The rental company charges more for extra service visits, so being prepared saves callbacks and keeps the route efficient.