be prepared
1. To remain in a state of preparedness for any unexpected or uncertain occasion that may arise. Popularized by the Boy Scouts of America, who use the phrase as their motto. It's a good thing I always carry a spare bicycle tube when I cycle to work. Like the Boy Scouts say, always be prepared!
2. To always carry a prophylactic (condom) or other means of preventing pregnancy or sexually transmitted infections, should an unexpected sexual encounter arise. A euphemistic appropriation of the motto of the Boy Scouts of America, "Be prepared." When you begin dating someone new, you should always be prepared!