Teach kids the importance of keeping a balanced bank account by making their grade depend on it! For the duration of my personal financial literacy unit, everything (going to the restroom, borrowing supplies, etc.) costs kids money, and they can earn money, too! If their account is in the negative at the end of the unit, they receive a failing test grade.
Students learn the value of keeping up with their money, budgeting, and not being frivolous. You'll also likely notice your classes' behavior improves, too!