Man, I can’t believe this is a question… you can’t think of things you like to eat?
A lot of your answer depends on what kind of diet you’re on, or maybe if you are just trying to eat massive, then you have a lot more choices.
If you don’t mind carrying a plastic container and a fork back and forth, make a salad and add some sliced chicken breast. Or fill your container up with steamed veggies, and top it off with sliced beef, chicken or turkey. You can eat this cold, or nuke it. If you are a skinny bastard, then make a pasta salad and add veggies, cubes of cheese, and slices of meat. (no packaged lunch meat… avoid anything too processed).
If you don’t want to carry a container to school, wrap a chicken breast in foil or plastic. Or make it a sandwich if you can use the carbs from the bread. Or a ground turkey burger. Add a banana or apple and a carton of yogurt. Or a ziplock bag of nuts. Or a hard boiled egg.
Use different spices and different recipes to add variety.
Look in some of the diet articles here for advice on what to eat, especially articles by Berardi and TC (who discuss specific food choices… maybe others do too). There are many recipe threads too, so do a search.
I personally get bored with eating the same food over and over, but you should be able to figure out a good lunch without too much difficulty.
When I was in high school, I was trying to get big. I’d bring a chicken breast sandwich and a couple of hard boiled eggs, and a banana. Then I’d buy one or two containers of milk.
Everyone thought my lunch was weird (this was the 70s, before bodybuilding was mainstream) but I put on 40 pounds in the course of a year (I started out as a skinny bastard, I went from 130 to 170).