i have the same problems with classes for college and i had it in high school too. Too hard to do strict diet so i didnt lol. Only advice i can give u is eat a good breakfast, bring lunch and dont eat school food. I would always eat before football practice too, i used to have brown rice with chicken and a fruit or nuts. Also drink alot of water. And of course clean up your diet, like bad fats, sugars and crap.
hope i helped ><