I just watched the final and have theories running through my head.

Regarding the Coffin, I guessed it as being Ben. He has no friends or family left in "the real world" as he has been on the island all his life. His mum died at birth and he killed his own dad. A couple of things point to this being Ben. A) No one showing up to his viewing/funeral. B) Jack being neither "friend or family", and Kate asking Jack "Do you think I would go to his funeral?" Or something along those lines.

Maybe Jack showed up because he has since realised that he was wrong and Ben wasn't the bad guy he has been made out to be? See how he desperately wants to get back to the island...

No offense there pinky, but this is the umteenth thread on the coffin, though, I agree, it is probably Ben.

Closed this see Season 3 Who is in the coffin

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.