I do rather feel this thread is verging on a lot of bollocks. If you have enough sense to go punting you should be able to decide whether to accept a drink or not.
I used to get offered a glass of wine more often than now. Becky Carlyle actually poured me a rather decent wine and it was only a half hour booking. A lot of fluffpots will give prossies wine or chocolates that they don't want, or at least not in that quantity, and it's more than decent to recycle some to the less grovelling punters I think.
A glass of water at least takes the taste of cunt away.
A cup of tea is nice afterwards if it's on her time.
For an outcall, I normally let her choose a drink, preferably shorts and mixer in a smallish glass unless I have wine open. She's welcome to reasonable tipples, as is any guest, but not as a time-wasting accessory.