Gold, user-modified, mini-maglite in leather belt-holster. Don’t leave home without it. The new ones that come with LED from the factory are almost an inch longer, so I am glad I got my hands on an early conversion kit :D.
Gerber or Leatherman multi-tool is invaluable as well. I NEVER go to a gig without both of them.
Although backlit controllers and computer screens make the light bit slightly less important while actually playing (in the old days you’d need the light to read the very fine print on the back of a CD sleeve or box), but like Terry stated: try finding something that fell to the floor.
Be interesting to see what design you come up with. Make sure you share it with us!
Greetinx,
Chuck