The Membership Card is a key item that appears in Kingdom Hearts II. It is an honorary card rewarded to members of the Hollow Bastion Restoration Committee, depicting Radiant Garden and the words "HBRC Honorary Member".
Kingdom Hearts II
Upon arriving in Hollow Bastion, Yuffie leads Sora, Donald, and Goofy to Merlin's House, where Leon, Aerith, and Cid are gathered. Yuffie introduces the group of four as the Hollow Bastion Restoration Committee. Later, after Merlin arrives, he reminds Aerith about the membership cards. Aerith explains that Leon thought Sora and the gang would like them.
After defeating the Nobodies in the Bailey and confronting Organization XIII, Sora holds his membership card out in front of him. The card then lights up, revealing the Keyhole and gate to the next world.