In a thread seeking advice/gifts to impart on a 9 year-old receiving his first wallet, MetaFilter member decathecting describes the ultimate reference card for young people:
Make a card that is twice the size you actually need. Fold it in half, and then write on both sides of what is now the outside. Tell the young man that this is his emergency card. Include on the card a telephone number that you promise to answer, day or night, if he is in trouble and needs an adult, no questions asked. Advice about stuff he can't talk to his parents about, help getting a ride home from someplace he's not supposed to be, bail money, whatever. Before you laminate it, slip a $50 bill between the two halves, inside the fold. Tell him it's there, and that it's his emergency money, and that it will always be there if he needs it, but that the money is a one-time offer, so he really needs to save it for a situation he can't get out of on his own.