in my gig bag is my bass... nothing more, nothing less!
however, i also carry a ruck sack with the following
3m two plug extension cable
two guitar-to-amp leads
two speakon to speakon connectors (from my amp to cab)
two power leads amp + spare
spare strings (never needed them to-date)
spare 9V
various alan keys
philips screw driver
strap
my amp has a spare fuse in the power socket
boss tuner & power adaptor
note pad and pen/pencil (ALWAYS!)
every now and then i carry a mic cable - in case i want to use it for some reason or other.. you know how it is?!
when i went on tour i took a soldering iron and solder too
I dont carry an books with me- if someone needs me to play a certain scale or outline a certain chord they can describe it to me thus "phrygian with #6" or whatever!?
I dont carry a spare strap cause i use leather ones and i've never broken one in 13 years!
I dont carry any mics, or spares for my amp - if the amp goes, it's through the PA, no bass or gig over!