The body of Jack's father is somewhere on the island, as it was being transported home by Jack on the flight. Jack has also seen his father on the island... maybe it
wasn't just a hallucination and an island pod-person is back impersonating Jack's father and performing drunken surgeries. Or not.
Casket... I too made the jump that it might be Ben in there. With the Boaters coming, perhaps the Losties discover that they need to reluctantly join forces with Ben to save themselves, in effect becoming "the Others". Jack obviously learns of the importance of the island, though belatedly. If Ben dies, especially if it's a consequence of leaving the island, Jack's last real hope of returning to it is gone, which is why he tries to commit suicide.
I could also see Locke being the one in the casket for the same reason. The rest of the Losties would still hold resentment toward him for trying to keep them on the island.
And my, Walt sure looks older than when Locke saw him a few weeks ago

(
THAT vision I didn't expect... what's the significance of it being Walt?)
Even though Hurley got sort of dumped on, I really like the fact that Charlie and Sawyer both were cruel to him only because they were genuinely trying to protect him. I also liked the fact last week that Charlie couldn't let his last words to Hugo be those comments about him being fat.
I agree with Ranger Wickett to some extent that if Ben hiked across the island with the idea he was going to change Jack's mind, I'd think he'd at least offer up some explanation other than "Trust me..." Though he did have a plan in place to try and force Jack to co-operate. Maybe that's just another example of how Ben's mind works... manipulation before explanation.