This poem originated in England first off.

Up and down the city road - a busy road with tailor shops along it
In and out of the Eagle    - The Eagle was a pub
That's the way the money goes - Spending money for beer in the Eagle
Pop goes the Weasel - A weasel is a tailor's iron sort of like a Sad
                      iron. Pop, is to pawn the weasel.

Unlike jobs today, tailors and other trades used to work by the week.
Each Monday they had to find a new job - up and down the city road -
This also applied to joiners and carpenters etc.
A good reference for British and American colloquialisms would be
a book by Eric Partridge titled "Dictionary of the Underworld"