This trick applies to every group of age..
For every time you can't go home for lunch, choose to eat at the school cafeteria than on the mall or restaurants.
For the most of the times comes to be cheaper to eat at school than in other place! Even if the meal itself comes to be a little cheaper, you may also spend in transports (in gas or tickets)!
Every time you this you'll save for a special occasion.. Or in some cases the rent for the little place your staying while studying!
If you have kids in school teach them to practice this kind of savings