(Disclaimer: Provider, not gentleman; just giving my take!)
I like to have some craft beer on hand just because... well, a good beer seems like it'd be incredibly refreshing to a certain type of fellow after a good energetic session.
Hardly anyone takes me up on it, just like hardly anyone takes me up on coffee or my cheese plate. But I kind of like bringing them along anyway--it makes it feel more like a well-rounded customer-service experience, lackadaisical and relaxing, and not ... well, something with all the intrigue of an oil change.
Some gentlemen will bring things as well. (Make sure you can open pop-top bottles! A recent gentleman brought a bottle of Framboise, but neither of us could open it.
I bought a nice-looking bottle opener that night, and hopefully won't have to run into that problem again!)
Teehee... and one of my favorite experiences so far involved the client bringing a bottle of Chambord and a bottle of Champagne (and three glasses), which combined well... OK, so the alcohol wasn't why I loved the experience, but... it was certainly a nice addition!
(If the gentleman brings it, I'd want it not to have been opened, granted, and may even wash glasses he provides. I figure most people don't want to roofie a girl, but it's probably something I should worry about more. So far, though...? The guys who've brought drinks have not only failed to roofie me, but also been amongst my most thoughtful!)