The Slumber Party Pals is a fictional series of books that appears in Hard Luck. There are about 100 volumes and Greg has read them all, stating that even though they are meant for girls, they are addictive, and once you read one, you have to read them all. Greg discovered the series during silent reading, but couldn't find anything to read. The first thirty editions were good, but Greg believes the later ones weren't so good, as the author started to run out of ideas. Greg states reading the Slumber Party Pals series is how he knows all about how friendships work with girls.