Okay, so the 'I thought you were dead' guy. I agree with people above who wrote that Clem didn't seem exactly happy to see this person. It can't be a person we've explicitly seen die in any variation of the story. And it's probably not anyone from 400 days, whom Clem has never been shown interacting with.
Lilly - I'm actually thinking she is a likely option. Sure, a lot of the players hated her, but TWD is notorious for having morally ambiguous characters. And having an antagonist is always good drama.
Molly - probably not. As said before she can potentially die in S1, and moreover, if she didn't, Clementine has no real reason to believe she's dead.
Kenny - yeah, maybe. Would be an anticlimax though, since it would be so obvious.
However, the person I'd bet money on to appear in Ep2 is....
Vernon. That's a person Clementine has a big reason to dislike (dirty boat-stealer!) and may have assumed to have drowned (via a little wishful thinking) after their escape from Savannah.