Even if Jack doesn’t die while guzzling beers and speeding to see Rebecca, he does get into a car accident that night that severely affects his life and ultimately leads to his demise. (And, because Kate urged him to make things right with her mom, she feels responsible.)
Jack arrives safely, if not soberly, at Rebecca’s first tour stop… only to see her in a close moment with Ben. Whether or not the closeness is real or just incredibly bad timing, what Mr. Pearson witnesses causes him to spiral out of control. He drinks more. He doesn’t take great care of himself. And ultimately, those factors contribute to his death.
A jealous Ben kills Jack. (Wow, things just got dark.)
A jealous Miguel kills Jack but, to this day, no one knows he did it. (Ooh, even darker!)
Jack is diagnosed with a terminal illness that advances rapidly and kills him while Randall, Kate and Kevin are still teenagers. (TBD: Why Kate feels responsible.)
Yes, Jack dies in some kind of accident. And yes, Kate feels somehow responsible. But just because the show juxtaposed Kate’s confession to Toby with Jack’s drunk driving flashback doesn’t mean that was the moment she was talking about. And this show does love to mislead us. (See also: the end of the series premiere, Kevin’s arrival on Sophie’s door, etc.)
No, seriously, this has got to be it: Jack perishes in a freak facial hair-grooming incident.