I am coming up playing my 6th tournament after returning to tennis at age 34. I used to be a real hotshot young player in the Juniors. Playing as an adult is a new ballgame for me. Sounds like you get plenty of time on the court. Go easy for a few days before tournament. Drink a ton of water. Bring a sports drink, energy bar and piece of fruit..banana's are my no brainer.
Most importantly I echo the other suggestions here to simply make sure you are enjoying yourself.
Playing half innergame, half winning ugly.