I never used to bring a back up.... after more than 40 years I hadn't broke a string, then played an outdoor gig about 3 years ago and broke a d string on a brand new (used) bass. My emergency kit was in the trailer, that a cop made us move to a lot 6 blocks away... I ended out playing the gig without a d string, the only thing the band noticed was that I wasn't doing any talking (normally it was my job to fill spaces with pointless babble...) All but the drummer didn't realize that I was spending every moment trying to figure out how to play around songs without using the d string. The drummer thought it was hilarious, the rest of the band was blown away that they didn't even notice. In my opinion,,, it was the worst string I could have broke.