money-bag (n.)

mid-13c., monie, "funds, means, anything convertible into money;" c. 1300, "coinage, coin, metal currency," from Old French monoie "money, coin, currency; change" (Modern French monnaie), from Latin moneta "place for coining money, mint; coined money, money, coinage," from Moneta, a title or surname of the Roman goddess Juno, near whose temple on the Capitoline Hill money was coined (and in which perhaps the precious metal was stored); from monere "advise, warn, admonish" (on the model of stative verbs in -ere; see monitor (n.)), by tradition with the sense of "admonishing goddess," which is sensible, but the etymology is difficult. A doublet of mint (n.2)).

It had been justly stated by a British writer that the power to make a small piece of paper, not worth one cent, by the inscribing of a few names, to be worth a thousand dollars, was a power too high to be entrusted to the hands of mortal man. [John C. Calhoun, speech, U.S. Senate, Dec. 29, 1841] 

Extended by early 19c. to include paper recognized and accepted as a substitute for coin. The highwayman's threat your money or your life is attested by 1774. Phrase in the money (1902) originally referred to "one who finishes among the prize-winners" (in a horse race, etc.). The challenge to put (one's) money where (one's) mouth is is recorded by 1942 in African-American vernacular. Money-grub for "avaricious person, one who is sordidly intent on amassing money" is from 1768; money-grubber is by 1835. The image of money burning a hole in someone's pocket is attested from 1520s (brennyd out the botom of hys purs).

I am not interested in money but in the things of which money is the symbol. [Henry Ford]

"small sack," c. 1200, bagge, probably from Old Norse baggi "pack, bundle," or a similar Scandinavian source. OED rejects connection to other Germanic words for "bellows, belly" as without evidence and finds a Celtic origin untenable. In some senses perhaps from Old French bague, which is also from Germanic.

As disparaging slang for "woman" it dates from 1924 in modern use (but various specialized senses of this are much older, and compare baggage). The meaning "person's area of interest or expertise" is by 1964, from African-American vernacular, from jazz sense of "category," probably via notion of putting something in a bag. The meaning "fold of loose skin under the eye" is by 1867. Related: bags.

To be left holding the bag (and presumably nothing else), "cheated, swindled" is attested by 1793. Many figurative senses, such as the verb meaning "to kill game" (1814) and its colloquial extension to "catch, seize, steal" (1818) are from the notion of the game bag (late 15c.) into which the product of the hunt was placed. This also probably explains modern slang in the bag "assured, certain" (1922, American English).

To let the cat out of the bag "reveal the secret" is from 1760. The source is probably the French expression Acheter chat en poche "buy a cat in a bag," which is attested in 18c. French and explained in Bailey's "Universal Etymological English Dictionary" (1736), under the entry for To buy a pig in a poke as "to buy a Thing without looking at it, or enquiring into the Value of it." (Similar expressions are found in Italian and German; and in English, Wycliffe (late 14c.) has To bye a catte in þo sakke is bot litel charge). Thus to let the cat out of the bag would be to inadvertently reveal the hidden truth of a matter one is attempting to pass off as something better or different, which is in line with the earliest uses in English.

Sir Joseph letteth the cat out of the bag, and sheweth principles inimical to the cause of true philosophy, by wishing to make great men Fellows, instead of wise men ["Peter Pindar," "Peter's Prophecy," 1788]