Origin/meaning of phrase “a martini for the rent”

I just finished reading Cornell Woolrich’s Rendezvous in Black (1948) and 2x in the book he has a character say he’s having “a martini for the rent”. I didn’t note the page numbers unfortunately so I can’t produce the exact context but I believe they were drinks ordered in a bar. I’m not finding any other uses of the phrase and I can’t guess at the meaning...except maybe because gin was once a very cheap, lower-class alcohol (though certainly not but the time of publication of this book)? Maybe it was a cute way of ordering a dry martini because vermouth is the pricier ingredient? Anyone have any ideas?

Nevermind. Skimmed the book for an occurrence and it was actually “A man came in and stood up at the bar and ordered a Martini, just to pay his rent.” So he ordered a cocktail he didn’t intend to drink as “rent” for his seat at the bar.