I quote from "The American Song Treasury: 100 Favorites", written/edited by Theodore Ralph, published by Dover Publications, Mineola, N.Y.

"'Pop Goes the Weasel' did originate in England centuries ago...[it] was quite popular...during the exodus of Pilgrims to America (1620-1640)."

"The song's title has nothing go do with a small explosion or an animal. The word 'pop' is British slang meaning to 'pawn' something, and 'weasel' was British slang meaning 'the tools of one's trade.' If a person were a tailor his weasel would be scissors, needles, thimble and tape measure, or a carpenter's weasel would be his saw, hammer, plane, and square. Therefore, the expression 'pop goes the weases' simply means one's money is gone and something will have to be pawned."

Assuming this to be correct, it appears that "pop" meaning "pawn" has survived to some degree, but "weasel" meaning "tools of one's trade" faded from use some time ago.