Way back in the early 80's, we used to get some "open bar" gigs, as much as you could stand. I can only remember one gig where the drummer took advantage of it and barely made through the show.
Now....not so much. Soft drinks, water and coffee are usually free, although some places put the coffee on at noon and offer it until closing time. Mmmm.
I bring a flask since I like a sip of Jim Beam every now and then while playing. Just a sip or two. I figure if I'm getting paid by some place to play, I just might get paid again to play there another time. I know a couple of bands that will never get that second call since they got trashed during the first gig. And some club owners do this on purpose to see who should get a second (or third) call. Oh yes, they do !