Kate seemed flabbergasted that Jack presumed she would want to go to the funeral. In my mind, that rules out any of the survivors.
Who was hated by everyone so much so that their funeral would not draw a single mourner save Jack? I really believe it's Ben and that Jack learned after leaving the island that he had a lot more in common with the little guy than he would ever had thought possible.
About tonight's episode, I think its interesting that future Jack seemed to have is life in order. He was clean shaven, working, made a drink with a tiny amount of alcohol and seemed to be quite adjusted. In last seasons finale, Jack was where Hurley was tonight. Maybe next week, we will see Kate and she will be the one wigging out.
Michael did kill a couple people after all. And you never know what happened after they got off the island. Maybe one of the survivors did something terrible. Who knows?