What does Sal always carry with her in an old pillowcase in the novel, The Year of Billy Miller?

The Drop Sisters are five similarly designed, pastel yellow whales that Sal owns and carries around in an old pillowcase. The oldest is Raindrop, and the other four (Dewdrop, Snowdrop, Gumdrop, and Lemondrop) were originally purchased by family and friends in case Sal ever lost Raindrop. But Sal discovers them in her parents’ closet one day, and adopts them all at once. At only one point in the novel is Sal without any of the Drop Sisters, and that is when she is on the front porch eating blueberries, so the Sisters will not get dirty.