Torn pages
In both Kingdom Hearts and Kingdom Hearts II, Sora, Donald and Goofy collect torn pages from other worlds to put these pages back into the book so the storyline can contiune. Torn pages are usually scattered in many worlds and only when all the pages are collected the keyhole of 100 Acre Wood can be steal.
In Kingdom Hearts II, the Heartless scatters the pages to other worlds as they were trying to steal the book from Hollow Bastion. when the pages were scattered Pooh lost his memories of his friends and all the places he knows like the Honey tree.
Sometimes when the torn page is complete an item appears such as a nature gem, treasures an such other things.