"Jumping Jack's Flash" is an orchestral piece from the Season 6 soundtrack.
Jack touches his father's coffin. He immediately remembers waking up on the Island.
Confused, he touches it again. He remembers running to the beach and coming upon the crash. He remembers reassuring a pregnant Claire and performing CPR on Rose, which reminds him of later resuscitating Charlie. He remembers speaking to Hurley for the first time and tending to Boone. He remembers conferring with Sayid, helping Shannon with her asthma and sharing Island knowledge with Sun. He remembers John Locke saving his life. He remembers Sawyer talking to him about Christian. He remembers phoning the freighter for rescue, and he remembers escaping in its helicopter.
Then he remembers Kate. He remembers her almost shooting him and laughing over the error. He remembers glass separating them in the Hydra. He remembers the first time they met, and he remembers kissing her goodbye.
He steps away from the coffin. Then he steps forward again and opens it. It's empty.