Riddle: Fox, Goose and a Sack of Corn

A man went on a trip with a fox, a goose and a sack of corn. He came upon a stream which he had to cross and found a tiny boat to use to cross the stream. He could only take himself and one other - the fox, the goose, or the corn - at a time. He could not leave the fox alone with the goose or the goose alone with the corn. How does he get all safely over the stream?