As banjomad pointed out, Cryril Tawney states that it is fried egg on fried bread. The queston was also asked at one of our chantey sings in S.F., so I wrote Cyril Tawney and asked him what it means. He pointed out that it would have been logistically difficult to make mass amounts of toast, so they made the fried egg on fried bread.
Chanteyranger