Whilst I took a lot of gear with me to cope for any eventuality, the only tools I used at my last 2 events were a set of Allen Keys, 2 x 10mm spanners and my all-purpose flathead screwdriver. I carry things like tin snips, mole grips, hacksaw, different screwdrivers, adjustable spanners, multimeter, soldering iron, and obviously my charging equipment. All of which fits comfortably in 1 toolbox.

EDIT: Oh, and a hammer .