There was a time when all that was needed was a guitar and off we went to play for whoever would listen. Now there are so many extra necessities, that we need to carry a first aid kit for guitarists. Here is a list of things I carry in my little first aid bag.
Set of strings.
Nail files (several).
Filing paper of several grades.
A ping-pong ball and super glue (nail construction set)
A pen, a pencil and erasor.
Tuner or tuning fork.
The footstool unfortunately doesn't fit in the little bag.