Operation Hydration is not just about drinking enough water and replenishing electrolytes. Staying healthy on the course, especially in high temperatures, also depends on eating the right way before and during play.
Eating the right way means eating the right foods and eating enough of those foods. A banana falls under the 'right foods' category, but the body is not getting all the nutrients that it needs if that is the only food you eat before a round of golf. You will want a variety of foods, rich in nutrients.
Dr. John Berardi of the Titleist Performance Institute's Advisory Board describes some examples of those nutritious foods in the following video and lays out the type of diet that will best prepare young athletes. A pre-round meal, be it breakfast or lunch, that incorporates Dr. Berardi's advice will better prepare you for a long round. On hot days that nutritious meal will make a big difference in keeping you energized and comfortable on the course.