+1 on what was already said, definitively relax!!!
And to be a bit more specific (and knowing that having a checklist can release some of the overwhelming stress of one's shoulder): (just my 2 cents)
- a stage plan (where is each musician) =>YEP
- a check list for each musician and for the group =>one for all should be OK plus everyone got his gear plus spare cables!!
- a (few) group rehearsal(s) that will exactly be the show => one
- individual rehearsals the day before the show => well you should all know your parts obviously

- sleep well before the show => maybe, but I guess Adrenaline will keep you awake even if your dead-tired
- stick the song list on the instrument (for the kb) => I prefer the floor version.
- bring a bottle of water (with sugar ?) on stage => 1L for everyone, these days maybe even more. No Sugar! In France they should serve you some nice food so no need for extra blood sugar.
- have some spare jack cables =>everyone should have his eq. including spare parts. For Keys, a DI just in case. Be sure to check what they have sound wise!!
- bring some adhesive to fix cables (Ruban à conduits in french, Gaffa in German or DUCT Tape in English, exactly!)
- know the amount of time we need to install and make "balance" (audio acoustic settings). The organizer will tell you that probably.
But ... I play very badly when I have pressure. I play smoother when I play relaxed. => So relax!!

One beer early the evening might help, others have different policies on playing on drugs (including alcohol) but that's another story...
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I would insist more than twice that you band mates are on time for the setup and soundcheck (bass player and drummer in particular

).
Any mos importantly, relax and enjoy!! Have fun!!