8 hours of school is a long ass time, ouch.
here's some suggestions:
at night, after school, whatever, take 20-30 minutes for food prep the next day.
chop up a bell pepper and throw it in some tupperwhere with a bunch of hummus. Combine with a protein shake and some olive oil. Also toss back an apple.
I'm sure you eat a good lunch and have that figured out.
I got this one from Berardi's book, I call it "Protein Turds" though because it looks like a turd, but tastes like a rieces pieces, so all is good. Mix up 4 scoops of chocolate protein and two big tablespoons of creamy peanut butter and about 1/4 cup of flax seed and just a little itty bit of water into a big bowl. mix the shit out of it, it should form into a thick paste after a lot of mixing (if not, you used too much water, if it doesn't mix well, incrementally put in a bit more). form it into bars and toss in freezer, there's about 1000 kcal total in that snack.
Turkey/cheese/lettuce wraps. it's self explanatory. Triple down on the lettuce though to get a little more veggies. snarfing down about 400-700 kcals on these isn't hard. I recommend pepper jack cheese.
I'm sure others will chime in with a lot more stuff. Also, you might wanna get an insulated lunch box and something to keep it all cool throughout the day. Making all that food for the next day will take about 10-15 minutes and another 5-10 to clean up.