Few non-guitarists know how crucial the fingernails are to the sound. They perform a function roughly similar to that of a clarinet or oboe reed (oboists, by the way, spend about half their waking hours making reeds). This is where the sound originates! So the shaping and care of the right hand fingernails is of the utmost importance. As I discovered as a young guitarist, the speed of your nail growth also can limit how much you can play. If you play more than six hours a day, your nails wear away faster than they can grow. When I was learning the Concierto de Aranjuez, which puts a lot of wear on your thumb and index nails, I had to find a solution. Turns out the best is to wrap a bit of scotch tape around the playing edge of the nail. It doesn't sound very good, but it prevents wear. Just remember to take it off when you play the concert!
Typical guitarist nightmares include breaking your thumbnail opening the stage door on your way to the concert and, one that has happened to me, opening your case just as you are being announced to the audience and finding your fourth string has snapped! You should always have an old, pre-stretched set handy. Luckily that didn't happen when I was playing a concerto, but at a private gathering of cast and crew at the Shaw Festival in Canada. I quickly replaced the string and went on to play, discreetly correcting the tuning from time to time.
Strings are the other big problem for guitarists. I hear that big-time rock guitarists have guitar technicians that replace strings and tune them up as needed. But I have always done that myself. If you are playing on a heavy schedule a set of strings will only last a couple of weeks so you can go through twenty-five sets in a year. The problem is the frets, which cut through the winding on the bass strings. Bowed string instruments don't have this problem!
I'm sure this is all terribly boring to non-guitarists, but all instruments have their secret lore. I once was trapped in a car driving from Vancouver to Seattle to play a concert and had to listen to two flute players discuss C# trill keys for hours and hours! Here is the first movement of a lovely Sonatina for flute and guitar by Castelnuovo-Tedesco that we played in that concert.