For staying power, I like to pair protein with fiber, and try to stay hydrated:
-mix a few almonds (protein/fiber) and dark chocolate (more antioxidants and richer flavor, so less is more) chips together - I keep mine in the freezer so the chocolate stays firm and fresh until the afternoon
-an orange (fiber) and string cheese (protein)
-one Chocolate Chip Cliff Kid Zone bar - yum! (tastes like a choc chip cookie, but packed with protein and fiber)
-2 homemade cookies (find a low fat oatmeal raisin recipe and add some flaxseed, nuts and a few chocolate chips) with milk
-fiber rich crackers (eg Wasa or Stoned Wheat Thins) and cheese
-yogurt (I like lowfat, rather than nonfat and look for lower sugar content) topped with fruit - whatever is in season, or some frozen berries
Good luck reaching your goal!
PS- if you like bananas, peel a ripe one and put it in your freezer before you go to school. When you get home, put it in a food processor and a dash of milk. Blend until smooth - it has the texture of soft serve ice cream. My kids LOVE this treat. We make sundaes by sprinkling a few chopped almonds or peanuts and chocolate chips over the "ice cream" and they go bananas! ahaha