I tend to go for a formula of 5 items.
1 main - e.g. sandwich, savoury muffins, pitta pizza, frittata, cheese and crackers, falafel and hummus, pasta salad, cold sausages or chicken drumstick
1 vegetable - e.g. carrot sticks, cucumber, tomato, olives, sliced pepper, sugar snaps etc
1 fruit - berries, apple, pear, kiwi.... whatever really!
1 dairy - yoghurt, cubes of cheese, cheese string
1 treat - popcorn, crisps, flapjack, biscuit etc.
They take a flask of water as it's the only drink school allows and either an orange or banana for snack time as it can be chucked in their bag and they don't need to open up their lunchbox for morning break.