a glass of milk and a bun

If Henry hadn't been determined to quarrel he would have taken her out to lunch first, and now she would have to go and have a glass of milk and a bun in a creamery with a lot of other women who were having buns and milk, or Bovril, or milk with a dash of coffee, or a nice cup of tea. It was a most frightfully depressing thought, because one bun was going to make very little impression on her hunger, and she certainly couldn't afford any more.

Patricia Wentworth

The Case is Closed (1937)

Not my favourite Wentworth - that is perhaps

 The Case of William Smith or Lonesome Road?

diluting the milk

He didn't know – he couldn't possibly have known – that in spite of all her economies, in spite of stinting and scraping, of eschewing meat, and eating margarine instead of butter, and diluting the milk, and buying the very cheapest tea that floated like dust on the top of your cup, Miss Buncle's account at the bank was overdrawn by seven pounds fifteen shillings and would soon have been overdrawn by more; for the dividends, which had been steadily decreasing, had now practically ceased. There were tears in Miss Buncle's eyes as she signed the receipt and folded up the amazing note. Fancy that tiny piece of paper representing so much! It really was rather astonishing (when you come to think of it) what that tiny piece of paper represented – far more than a hundred sovereigns (although in modern finance less). It represented food and drink to Barbara Buncle, and, perhaps, a new winter coat and hat; but, above all, freedom from that awful nightmare of worry, and sleep, and a quiet mind.

D. E. Stevenson

Miss Buncle's Book (1934)

Some thoughts here.