Always have your backups
I always try to be two steps ahead. I always take multiple computers with me to events. 2012 was the last time I had a beach ball on my mac on my external hard drive and it took like a minute but have had not other issue since. The next day I ordered another mac book pro and no longer use an external hard drive but an internal hard drive. Not only computers, I take I do take multiple set ups too since I always like being prepared. I am grateful for controllers since it is turntables and mixers all in one.
I have a big suv that I fill it up to the brim with equipment. I believe in having back ups to my back ups. Yes, it is more work to carry everything but it is for a piece of mind. I was talking to another dj that only carries one controller and one computer. I asked him what happens if something does not work. His response was oh well. I do not do oh well. If for some reason my computer is not working, I have another one with the same music and I will have the playlist on my phone. Say my controller goes on vacation, and then I have another one who is ready to be on the starting line up.
One never knows what to expect at a gig. One gig may not have electricity at a close proximity or extra speakers maybe needed. I have speakers on the bench waiting to wave them in.
A lot of events that need djs are special days and everything has to be run smoothly. Every little detail counts to make your special day even more special. Be prepared at all times!