DDs are at primary school and I go for five items as it's an easy formula for me to stick to. They have a bottle of water for their drink.
1 main - could be a sandwich, or pasta salad or some cooked chicken, or homemade sausage rolls, or pizza pinwheels, or cheese and crackers, or cut up sausages or falafel and hummus.
1 vegetable - carrots, cucumber, tomatoes, olives, sugar snaps, edamame etc
1 fruit - loads of options here, I just try to vary it a bit throughout the week
1 dairy - yoghurt or cheese
1 treat - flapjack or homemade pancakes or crisps or popcorn etc
I batch make lots when I have time and freeze. My "sausage rolls" are turkey mince blended with carrot and courgette and I just make a couple of trays worth at a time and store in the freezer. I always make packed lunches the evening before when I'm prepping dinner so I can just take items out of the freezer and put their lunchbox in the fridge ready for the morning. It makes life a whole lot easier! As does having two lunch boxes per DD so I always have one to pack if the other one is in the dishwasher.