I'm building mine into a wiring cart for wire spool storage, tools, connectors, etc. I can roll it out to the job instead of going back and forth.
Other ideas for handtrucks / 2 wheel dollies:
Mobile air tool stand. Long air line, a few frequently used air tools on the rack, adapters, air tool oil, penetrating and cleaning solvents in spray cans on a rack, etc.
Welding Companion Cart: Mount PVC Pipes (capped) for storage of your welding rods to keep them dry and contaminant free. Good place to keep your filler wire for TIG welding as well. Maybe put in a rack for holding C clamps, welding pliers, mask storage, magnets, welding jacket and gloves.
Mobile Shade / Car Wash Detailing Stand: Mount a small shop vac to the bottom, put in a nice long extension cable storage, hose and accessory storage. A couple of trays to hold car wash, rags, sponges, maybe your pole-mounted wash brushes in PVC tube mounts on the sides. Mount a piece of tubing on the side to place a patio umbrella on it to provide shade where and when you need it. Just that alone may make a very nice addition for driveway wrenching to have a shade where you want it.
Battery Charging / Jump Station: A car battery on the bottom with a battery tender connected to keep it topped off. Jumper cables wired to it permanently, ideally with a switch in line with the ground to disable any possible shorting. Mount a good sized battery charger and extension cord to do charging of batteries at the vehicle side. Include a tray to hold battery terminal cleaners, brushes, proper pliers, test meter and a simple test light.
Look around your garage and you can probably find several things that could benefit from becoming a mobile work station that can be moved to where you need it.