Eating junk food and sugar and drinking soft drinks will not fuel an athlete and could ultimately cause damage because the nutrients are not available when needed during the competition.
Training for any sport is a huge factor determining whether or not an athlete will be successful. One of the biggest mistakes an athlete or a coach can make is not utilizing the principle of specificity, where the training must match the physical demands of the specific sport.
Volleyball is an anaerobic or stop and go sport requiring quickness, jumping, agility and explosiveness. These types of activities require fast reaction time; movement speed and utilizing fast twitch muscle fibers.
The physical training for volleyball needs to match these demands, so jumping activities, sprints and agility drills are important for success.
However, I have seen many athletes and coaches train the slow-twitch muscle fibers by doing mostly long distance running and slow drills where the athletes are not challenged by the intensity and speed they will most likely encounter during a competitive match.