If you want food that is easy to pack and filling, I suggest compressed biscuits are better

If you think the compressed biscuits are too dry, you can buy bagged milk tea to eat together. And both of these are conveniences. Even if the teacher doesn't allow you to bring food, it's easier to hide when checking the dormitory.

If the teacher brings food, you can pack some bread or instant noodles.

If you like sweets, you can pack a few pieces of chocolate or high-calorie foods to keep you full