The waiter: "Hello sir, what would you like to drink?"
Sir James: "I'll have a brandy"
Is still correct/common in English if Sir James answers:
"I have a brandy" (without "will")
I know I can say: "I have a brandy every saturday night".
The waiter: "Hello sir, what would you like to drink?"
Sir James: "I'll have a brandy"
Is still correct/common in English if Sir James answers:
"I have a brandy" (without "will")
I know I can say: "I have a brandy every saturday night".
In response to the question
Hello sir, what would you like to drink?
If Sir James answers
I will have a brandy
it means he would like a brandy to be served to him, in the future
If Sir James answers
I have a brandy
he is telling the waiter he already has a drink, in the present
Sir James has a brandy every Saturday night.
Sir James will have a brandy every Saturday night.
are both correct since it is a repetitive action of drinking brandy.
My wife goes shopping every chance she gets.
My wife will go shopping whenever she is in town.
I'll have a brandy tells the barkeep to bring the speaker a brandy. So you would use this to order a brandy.
I have a brandy doesn't tell the barkeep much of anything. S/he might wink and ask if you'll have another. It could imply since I already have a brandy, I don't need another now. So, no you would not say this if you want to order an initial or another brandy.
I'm having a brandy tells your friends what you have ordered or plan to order. (It is like I'm going to have a brandy.)
You could also use this to order a brandy, but usually only when telling the barkeep/waiter what you are having as well as what your friends are having. Well, let's see, I'm having a brandy and Brandi is having a whiskey soda and Martin is having a martini. Here you are ordering a brandy "indirectly" by telling the server what everyone wants to have. This usage is not so pragmatic if you are by yourself.
You could say I'll a brandy have and be understood, if a bit lyrically.
Take Peter’s answer first, but “I have a brandy” often means “I’ll have a brandy, but I’m too lazy to use the English language properly”.
So unless you hold a brandy in your hand, if you tell the barkeeper “I have a brandy”, he or she will serve you a brandy. They might ask “one brandy?” to make sure there is no misunderstanding.