International Dollars Puns

Years ago my parents sent my sister to England for a summer camp/study trip. Whenever we would call her we'd all gather around the speakerphone and talk briefly since international phone calls were expensive back then. One day we call her and my sister tells my dad that she has 6 more days of camp left and she is down to her last pound (dollar). There is a long awkward pause. Then my sister ask: Dad, what should I do? To which my dad responds: Spend it wisely...