The closest I come to a "gig" is our annual big festival. By coincidence I've just been reviewing my packing lists and find that what I took to the last WVA festival included:

Box end wrench sets, inch & metric
Open end wrench sets, inch & metric
3/8 & 1/4 drive sockets, inch, metric, std & deep
1/2 drive socket set and torque wrench (in blue toolbox)
Crescent wrenches, 6" & 8"
Pliers, slip joint, two std size
Pliers, Needle Nose, two std size
Diagonal cutters, two std size
Wire strippers, one EZStrip
Crimp pliers, one good set
Micrometer Calipers, metal 0.001"
Micrometer Caliper, plastic, 1/128"
Hex wrenches, inch & metric
DrillNDrive wood csk kits/loose (select a set, with spares)
AC Drill motor, 3/8 drive
DC Drill motor, 3/8 drive with charger
Drill Index, small set blue box
Spade Drill assortment
Drill Index, large set red box
AC sabre saw
AC sabre saw blades assorted
Hand hacksaw
Bolt Cutters, small & medium
Claw hammer
Small ball peen hammer
Plastic mallet
VOM
Outlet Test Plug
Water pressure gage
Tire pressure gage(s)
Spring Scale, 50 lb or better
Razor Blade Scraper with spare blades
100' Survey Tape (or longer of two)
Air Compressor, tires
Air Compressor low P hi-Volume
Spare Screwdriver Bits
Adjustable Square
4' straightedge
Small Carpenter Square
3" C Clamps x6
1.5" C Clamps x6
Dremel with accessories
Pickup Magnet, extendable
Inspection Mirror(s)
Magnifiers (3)
Fuses, assorted to match Camper & Vehicles
Lamps, assorted to match Camper & Vehicles
Bolts, assorted #6 thru 1/4
Washers, assorted #6 thru 1/4
Fender Washers, assorted #6 thru 1/4
Rubber Fender Washers, assorted #6 thru 1/4
Nuts & Wingnuts, assorted #6 thru 1/4
Fender Washers, assorted #6 thru 1/4
TyWraps, assorted, mostly 7" okay
Tire Valve Caps and Cores
Hose Washers
Hose Restrictor Washers
Wood Screws, #8 FH & RH Phillips
Wood Glue
PVC Cement
ABS Cement
Contact Cement
Silicone Grease
Silicone Spray
Hitch Ball Grease
Awning tiedown straps, stakes, hooks
Awning deflap clips (need better than present)
Battery Charger
Waste Cart with tow hook and service hoses.
Mag Sweeper
Wheel Chocks, 4 minimum
Std Service Cord
Spare Service Cord
Waste water deodorant, 6 dose minimum
Tire pressure gage(s)
Water Pressure Limiters, 2 ea
100' 1/4 or 5/16 nylon rope
100' nylon twine
30" Clamps x3
Outlet test plug
Hose Tee x4
Hose Outlet w/ shutoff x2
Fluorescent Trouble Light x2
25' extension cord x3
15' multitap cord x2 or x3
House & Garden Insecticide
Insect Repellant
250' AWG10 Extension Cords
200' AWG12 Extension Cords (100' x2)
50' AWG12 Extension Cords x1 or x2
25' AWG12 Extension Cords x4
200' Water Hose
Stepladder
Waste Water Cart
Instruments: (Mandos, Dulcimers, Whistles, Harmonicas, Concertina, Tub Bass, and miscellaneous)
Music Stands
Lawn Chairs x4
Folding Chairs, wood, x4
Folding Chairs, metal, x2
Picking Stools, x6
White small tables x4
White large tables x3
Shade Tarp(s) camo
Laptop with Printer/Scanner & consumables
Cameras, 2x film + 1 digital
Suitcases x2 usually
Leveling blocks, to 6" inches for 2 wheels

ALL ITEMS ON THE LIST WERE USED AT SOME TIME DURING THE MONTH WE WERE THERE.

(Decorations, like her gargoyles, rope lights, signs, bubble machine, etc were omitted from my review for the present.)

For a more ordinary "gig" the only additions I'd probably add to the lists already offered by others would be a small magnet (for finding the little screws and such that fall into cracks) and perhaps a decent magnifying glass (for reading the fine print in the contracts).

John