What is the symbolism of Clemantine's Minnie and Mickey backpack?

Clemantine's Mickey and Minnie Mouse backpack symbolizes imagination. After Claire's friend gives Clemantine the backpack for her birthday, she becomes attached. She carries it everywhere she goes, filling it with rocks she plans on giving to Pudi when they are reunited. The backpack allows Clemantine to imagine a future beyond her present reality, to hope for a world in which her family is together again. She better understands its significance when she visits Disneyland years later.