The brandy and soda is a drink that seems to exist today primarily as a P. G. Wodehouse reference. It’s a basic combination that nevertheless occurs to no-one but those imitating Bertie Wooster. Surveying the internet, it appears that mention of the ‘B and S’ without reference to Jeeves and Wooster has been strictly outlawed. They do seem to be rather a Wodehouse special—Penguin describe their anthology of Wodehouse on drinking saying:

His imperishable writing displays a well-turned appreciation for all kinds of booze – cocktails, champagne, port, whiskey and brandy (with soda, of course) …

But Wodehouse doesn’t have a monopoly on the combination. Pynchon (whose appreciation for booze I would argue far surpasses “well-turned”) gets in on the rather stuffy B n’ S action in one of his first published stories, “Mortality and Mercy in Vienna.,” and then again 47ish years later in Against the Day.

“Mortality and Mercy” is Pynchon’s only published early story not included in Slow Learner. An anecdote (albeit a somewhat secondhand one emerging from a postmodern hall of textual mirrors) recorded here suggests that Pynchon wrote the story in an undergraduate class at Cornell in response to a first sentence provided by the professor. I will decline to summarise the plot and instead only endorse it as being a fun read and provide you with this one relevant sentence:

He would stand, therefore, out in some street, not moving, hanging on to the briefcase and thinking about Rachel who was 4′ 10″ in her stocking feet, whose neck was pale and sleek, a Modigliani neck, whose eyes were not mirror images but both slanted the same way, dark brown almost to fathomlessness, and after awhile he would drift up to the surface again and be annoyed with himself for worrying about these things when the data inside the briefcase should have been at the office fifteen minutes ago; and realize, reluctantly, that the racing against time, the awareness of being a cog, the elan — almost roguery of the playboy element in the Commission which went well with his British staff officer appearance — even the intradepartmental scheming and counterscheming which went on in jazz cellars at two in the morning, in pensions over brandy and soda, were, after all, exciting.

That passage almost undermines the above about brandy and soda existing only as upper class British affectation, except that it does still seem to be tied to his “British staff officer appearance,” does feel a part of the Commission’s toffee old-timey culture he fits so well.

In AtD, the brandy and sodas are again hovering in the vicinity of Britishness itself, this time expressed in the persons of who else but Neville and Nigel. They’re at a performance of Waltzing in Whitechapel, a somewhat meta “musical comedy about Jack the Ripper” (p. 679). At intermission, they run into a Colonnel Max Khäutsch, encountered earlier in the book escorting Franz Ferdinand. N&N are mostly drinking cough syrup out of a flask, but Khäutsch is getting into the local spirit “working on a brandy and soda,” (p. 680).

“Working” ain’t wrong—this thing is no fun. It tastes like a visit to grandma’s house. (Not my grandmas, they’re cool grandmas. A hypothetical stereotypical attic-dwelling cobwebbed grandmother.) Dusty, musty, staid, and dull. I may have mixed it too weak, but really very little promise was showing. I can’t say I’m surprised the brandy and soda has been relegated to affected Britishism status.