The reference to the Prodigal Son is a reference to a story about Jesus that is in the Gospel of Luke in the Bible. It is tied to Lent, also tying it to the Mardi Gras theme in the book.
The reference to Pygmalion and Galatea is a reference to a Greek story. Pygmalion falls in love with the statue he carves, Galatea. Gisselle is essentially told to help reinvent Ruby so that others will be impressed by her transformation from Cajun girl to a young woman of Daphne's standards. In this metaphor, Gisselle is Pygmalion and Ruby is Galatea.
Casket girls are the women brought from France to Louisiana to be married. The women carried their belongigns in cassettes, also referred to as caskets. The girls were chosen from orphanages and convents because they were most desirable as virgins. Descendents of casket girls are generally proud of their heritage.
At one time, Storyville was the red-light district of New Orleans. The name Storyville came from the name of the man who created the district, Sidney Story. The district was officially shut down in 1917 and in the 20s was full of gambling joints and other forms of entertainment. Most of the buildings that were built during these days were torn down in the 1930s for a housing project.