Make sure you get good amounts of sleep in before the tournament. Make sure you stay fresh and hydrated because three games in two days will tire you out quick. So staying hydrated will help in the long run when in the third game on Sunday you are fresh and aren't cramping up. Stay away from the sodas if you don't already.
Yea just eat right and rest up. Trying to get more fit will only make you too tired by the time of the tournament. NO SODA!!!!!!!!!!!!!!!!!! (OR DAIRY THE DAY BEFORE AND DAYS OF THE TOURNAMENT)