Teaching them that there has to be more money coming in than going out is critical, as is defeating the illusion that credit cards are magic pieces of plastic that allow you to get things for free.
When you are trapped on a coach or in a plane or in sunny climes with 20 millionaires, one of two things will happen: the conversation turns to women -- and, by extension, wives -- or, as if by magic, somebody produces a pack of cards.