Dear God, he could use a drink. Or a thousand of them. (3.65)
Jack has thoughts like this quite often. He has this particular thought after his first meeting with Watson, in the cellar, where he gets his big warnings about the boiler. The novel's explosive ending is foreshadowed heavily here, and throughout.
[…] the Bad Thing. (4.6)
The Bad Thing is what Danny calls his father's drinking. Do you think Wendy gave it that name? In any case, we can tell that Danny is less terrified by the Bad Thing, than DIVORCE, because DIVORCE is in all caps. Danny's isn't afraid of the bad thing; he's more concerned with the pain the desire to drink causes in Jack.
"Jesus, Al. We ran him down. I felt it." (5.29)
We think this passage informs Jack's character. He's totally smashed, but it's Al whose driving the car that hits the mysterious, child-sized bicycle. Yet, Jack shares the entire responsibility for the incident, even when he's sure they hit a child. His guilt and fear over the event causes him to immediately stop drinking.