There is a lot of drinking in the Godfather trilogy, and there is barely a scene in any of it where there isnt wine sitting around. There are many instances where people are offered a drink just before they get killed --- I can think of this being used many times, and invite others to point out similar scenes -- for instance Sonny tells Paulie to drink some brandy for his "cold,"and Michael gives Carlo a drink to calm him before he confesses.The hit on Pentangeli is in a bar, as is the one where Tattaglia Jr. offers Luca pre war scotch.I get the sense, however that both Vito and Michael Corleone take a dim view of alcohol consumption, or at least too much of it. There are many many times when Michael is offered a drink, and he has a glass of water or a club soda. As for Vito, I thought there was a hint of disparagement in the scene where Hagen is gathering himself to break the news of Sonny's death ...."But you needed a drink first....all right, now you've had your drink, now tell your Godfather what everyone else already seems to know." I also thought the Godfather felt somewhat sorry that in his declining years he was drinking more wine than he had in the past, and Michael, knowing that Vito's time is almost up says, "Thats all right pop, its good for you."
On the other hand the weaker characters always seem to need to have a shot of something or other. Fredo always seems to need a drink. Merle, Connie's boyfriend needs one just to sit with Mike.

In the book Puzo stresses how moralistic Vito Corleone was, and some of this comes out in GFI, but I wonder if this rigidity applies to booze.