The day before Thanksgiving, most of the lines you see around the country are at grocery store checkouts, as people hurry to pick up last-minute ingredients. But if you walk down Wickenden Street in Providence, Rhode Island, on the third Wednesday in November, you’ll see a line of hungry customers down the block waiting for the most popular slice of pizza all year long. Every year, for one day only, Fellini’s Pizzeria offers its famous Thanksgiving Pizza, topped with classic items from the holiday dinner table. Unorthodox among both pizza parlors and Thanksgiving celebrations, the unusual combo has inspired cult...