We have to send fruit for fruit break, lunch and a snack for recess.
In summer you can make sandwiches for the week on Sunday night and freeze them. If you put a frozen sandwich in the lunchbox in the morning it will be defrosted by lunchtime. Sushi balls can freeze too and so can yogurt.
DS2 seems to eat half his lunch after school because he's so keen to play that he only eats what his teachers make him eat which is generally a sandwich or a sushi ball.