Normal minimal guitar players' equipment ...

Guitar
Spare strings (£4.99 el cheapo set, will get me home in case of a breakage)
Tuner
Tobacco tin, containing picks, capo, bottleneck
Duster (used to wrap the tin, soften any sharp edges; also wipe sweat etc from the neck and strings every so often)
Several A4 sheets of lyrics
Reading glasses in case I need to use one of the sheets
Tin of John West's tuna in mayonnaise

This last is waiting opportunity to be deployed when some improvident player says, "Can I borrow a tuner?"