In Ireland, where alcohol is such a large part of life, there is very little variety in the kind of drinks people drink when they’re out, and as a result a drink isn’t expected to say much about the drinker. Men drink pints. Women drink wine or vodka with a mixer.
Drinks matter in The Godfather II.
Fredo is “weak and stupid”. It’s illustrated in his choice of wife (she gets drunk and falls on the dance floor at Michael’s son’s communion), and it’s illustrated in his choice of drink. Most likely to say “it’s refill time”, he orders banana daiquiris.
Michael Corleone – more likely to say “if you think like the people around you then anything’s possible” – always seems to drink a club soda: because he is detached. The club soda expresses detachment and is the strongest expression of contempt for his brother’s weakness and lifestyle.