I suspect this will be highly variable. At one extreme you might have @corporate-wage-slave and the other this legendary report from @macabus: 8 bottles of Dom from LAX-BKK on SQ in F

Personally, at present any business class travel is leisure-based, so I will usually have a drink or two. My most recent was a PRG-DOH-PVG and return. The outbound was well timed for PDB of champagne, wine with the meal, and post-meal whisky before Doha. The onward connection also involved some wine and a whisky (I think, my body clock was a bit screwed at that point). By contrast, the return from PVG involved nothing at all, as it was 1am and I was exhausted. I made up for this with a 4am espresso martini in Doha...

Conclusion? Too many variables: flight length, time of day, what one is doing the next day, what company one is in, general “do I feel like alcohol” mood, etc.