Always keep a tube of Krazy Glue or another brand of cyanoacrylate super glue handy in your gig bag. While it has literally hundreds of uses, a good reason for guitar players to have handy is to repair broken fingernails for players that have a finger picking style. A broken nail can hinder your performance in this style. Another good reason is in the event you tear a callous on your fretting hand. The late great Stevie Ray Vaughan was known for gluing his torn up fingers back together on occasion with super glue. And a last interesting point is that cyanoacrylate super glue in a spray form was used beginning in 1966 during the Vietnam War. The spray was used by medics to close wounds and stop bleeding so soldiers could be stabilized to transport back to a base hospital. Hopefully guitar players will not have to use it for such extreme measures on a gig. There is more information in the article “Gig Bag Essentials” here.