I regularly volunteer to do electronics repairs during a local Repair Café. This is a checklist of stuff I take with me:

Tools:

• laptop, handy to look up datasheets, manuals and repair videos
• screwdrivers: flat, philips, torx, special. Best to take torx screwdrivers, bits do not always fit
• side-cutters, assortment of pliers
• smartphone repair kit
• multimeter, ESR meter
• audio cables: mini-jack to mini-jack, mini-jack to cinch/phono, mini-jack to jack
• USB cables
• adjustable power supply with leads
• leads with crocodile clips
• helping hands
• mains extension cord and power distribution
• glue gun
• soldering iron. I actually use a gas soldering iron, handy to use the exhaust for heat shrink
• dremel
• drills
• some additional lightsource
• solder wick

Consumables

• canned air
• contact spray
• machine oil
• cotton swabs
• (charged) AA, AAA and 9V batteries
• wires: different gauges, solid, stranded, flatcable, coax…
• audio cables (from broken headphones and the like)
• solder
• super glue
• two component glue
• heat shrink tubing
• sugru
• zip ties

Components:

• little loudspeaker (not everybody brings their speakers with a defective amplifier)
• mains power leads with and without ground
• glass fuses
• resistors
• electrolytic capacitors
• diodes
• connectors: barrel jacks and sockets, stereo headphone jacks (3,5mm) and sockets
• metric bolts
• switches

I will probably add stuff to this list in the future.