Carmela is humming while in the shower. The tune is from the Italian song that she and Furio danced to at his housewarming in episode 4 The Weight.
The expression "mind your p's and q's" actually refers to printer apprentices being mindful that p and q looked similar on press blocks. The pub owner origin myth came much later.
Tony listens to Eclipse and then is singing Another brick in the wall (part 2), both songs from Pink Floyd.
The book Carmela is reading while in bed is "The Mists of Avalon" by Marion Zimmer Bradley. The book follows the trajectory of Morgaine, a priestess fighting to save her Celtic culture in a country where Christianity threatens to destroy the pagan way of life.