pin money

(idiomatic, dated) A relatively small sum of cash kept in one's personal possession, for routine expenses or incidental purchases; an amount of money which is not particularly significant. [from 18th c.]

Example: 1723, Charles Walker, Memoirs of Sally Salisbury, VI:
  Damn you for a Son of a Bitch! Shall you wear such Things, and I want Pin-Mooney?
1813, Jane Austen, Pride and Prejudice, ch. 59:
  Lord bless me! only think! dear me! Mr. Darcy! . . . Oh! my sweetest Lizzy! how rich and how great you will be! What pin-money, what jewels, what carriages you will have!
1886, George Gissing, Demos: A Story of English Socialism, ch. 27:
  [H]e practised economy in the matter of his wife's pin-money.
1911, David Graham Phillips, The Conflict, ch. 7:
  But these sums were but a small part of their income, were merely pin money for their wives and children.
1921, Baroness Emmuska Orczy, Castles in the Air, ch. 3:
  Certain it is that out of the lavish pin-money which her father gave her as a free gift from time to time, she only doled out a meagre allowance to her husband.
1892, Mark Twain, The American Claimant, ch. 3:
  "Money—yes; pin money: a couple of hundred thousand, perhaps. Not more."
  Washington's eyes blazed.
  "A couple of hundred thousand dollars! do you call that pin money?"
1912, O. Henry, "A Ruler of Men" in Rolling Stones:
  "Where is Reddy McGill now?" . . .
  "Putting up windmills in Arizona. For pin money to buy etceteras with."
1917, Christopher Morley, Parnassus on Wheels, ch. 3:
  "[T]he housekeeping accounts fall to me. I make a fairish amount of pin money on my poultry and some of my preserves that I send to Boston."