I actually avoid all contact to chess the same way i avoid contact with school content on the very day i do exams in university, as i want to avoid for new "data" to confuse me in a most important exam, and it seems to work out good.
But unlike you, i don't have a "preset" opening and instead i like to play different openings against different players in a way to adapt to their gameplay and not the opposite.
If i play against a kid or a veteran, it's most likely i won't engage in their openings no matter what, because those two "tiers" of players usually know their game to exhaustion and know most of the traps and middle game to it, while i prefer to take control of games with gambits if needed , and try to force the opponent to play "my" game.
If i play against stronger players than me, i usually end up starting with more exotic openings like Indians, 3 pawn systems or something for the likes, so that i'm not also auto-lost if i happen to play an opening they're most used to play against.
I gotta go with exercise on this one.
I'd say plan your opening (if you're white) and plan your defense against a king pawn opening. Or at least play two or three games right before your game or tournament. Have a jog and wake up and play.
I even like to really get in the feel of it and study a chess book that morning all the way up to game time.
What's all of your pre-game routines?