Don’t change your strings before the gig – have an hour of practice at least between string change and gig.
If anything uses batteries – pedals, wireless, etc. Use fresh ones or KNOW they are “near-fresh.”
Know who starts all the songs on the setlist, and HOW they are started (4-count on the high hat, etc). Practices leading up to the gig should be practicing the gig, including between-song conversations, intros , etc. This is IMPORTANT until you get CRAZY comfy as a band being looser.
All stringed instruments should get a final tuning check at the closest moment to going on as possible. Make sure everyone tunes the same way – if guitarist A uses “sweetened” tuning, make sure other guitars and bass do, as well.
At the gig, ALWAYS make sure you or someone you trust implicitly has an eye on the gear AT ALL TIMES. Keep your band’s gear together in one place.