I could make one suggestion. Many people grow exhausted throughout the day and will resort to coffee, sugar, or naps. However, in my experience caffeine and sugar do not wake me up, and naps are not always an option. But, having enough protein always manages to keep me awake and remotely energized, even after little sleep the night before. Having enough meat, eggs, etc in a meal can provide you enough energy to remain active throughout the rest of the day.

However, if this still does not work, or if you simply have no access to a source of food, then I could make one more suggestion. This one should typically only be an infrequent choice, but if you can, you may be able to skip a few classes, so long as nothing major occurs. But I would advise the former option where possible. Just remember that your health should always take top priority.