My gig bag contains: guitar cables, patch cables, mic cables, midi cables, various adapters [XLR-1/4, 1/4-RCA..etc] and Y-jacks, wire, 1/4 jacks, soldering iron + solder, black tape, circuit tester, multi-meter, extension cords, power cords, AC adapters, batteries, strings, picks, cowbell, caffeine tablets, Tylenol, Rolaids, nasal spray, eye drops, and cough drops.
If something screws up so badly that none of these thing can fix it, I put $20 in the jukebox and go home.