Understand that this is second hand info. I’m not a standup, just an interested hobbyist

It varies, and there’s a difference between club comics, touring comics, and the big names doing sizable venues.

Your typical local comic that only works one or two clubs, they’re often drinking water or soda, and it’s a gimmick to sell drinks they get a cut of, though that cut might be tiny. They don’t get paid enough to really drink between sets, and they would absolutely be paying for any booze they have on stage.

Your touring comic, the ones that are usually doing clubs and smaller venues across a country, is usually the same basic idea, but you will run into them having something they prefer over water or soda. They tend to have longer sets, even in clubs, and only one set a night. So they don’t have to worry about drinking too much and fucking their act. Not that a lot of comics actually minimize drinking, but the serious ones keep it to a minimum when they’ll be on stage and save any hard drinking for after. So you’ll see some beer, maybe the occasional mixed drink.

The big names, they have more freedom, and longer sets. Think someone like maybe Larry the cable guy, on up in drawing power to where Eddie Murphy was in the eighties. Popular enough to put butts in seats solo in arenas and bigger auditoriums. They drink whatever the fuck they want on stage. They tend to pick things they either enjoy, or will keep their throat and mouth in good form. Ron White was kinda well known for scotch and other whiskey on stage, but he’d be sipping at it, and the ice was diluting it over his shows. But most of those comics err more on the side of lubricating the pipes than anything else.