I'm putting this here because I have no idea if what I'm saying here is true. It's just something I came up with so it's "fiction" (note the big fat quotation marks) and my aim is to entertain (sort of), so I figure that qualifies it as "creative." Just thought I'd let you in on my thinking before it gets moved.

Anyway, I just thought that the reason the term "break the bank" came about is because way back when, in like the 1700-1860's when Britain had "das uber navy," Britain would pay it's sailors with grog. (This is actually true, you can go look it up...No, SERIOUSLY! Go check Wikipedia or something! ) Now grog, if you didn't know, is an actual type of drink that is basically a 10 pound keg of rum added to 40 pound keg of water. This served three purposes:
1.The rum back then was like 90 proof, so it acted as an antibacterial agent, and
2.The alcohol also makes one drunk; useful if you're spending 6-24 months in a confined space with 40 other guys that don't bathe, haven't, nor plan to anytime soon, and your job consists of hard physical labor, where if you screw up, you could get whipped or killed.
3. the first two qualities made the stuff rather valuable, hence it's use as payment at sea.

This is not to say they did not get monetary compensation for their labor, but that payment was given at the end of the voyage; Grog was more of a "daily payment."
(which probably also spawned the term "[to] stay as long as the rum holds out" as to mean "work as long as, and only as for as long as one is being compensated in some form." Certainly rolls off the tongue better.)

Now I'm willing to bet that those sailors had little flasks, that if they were clever, and frugal, would hold a small portion of grog. This could then be used as kind of an underground currency; enabling one to get a good or service, with out giving up any of their Farthings or Pence at the end of the trip.

NOW this only works to fuel an "economy" as long as no one actually drinks it. Hence they would usually be sealed with a cork, or some other stopper, most likely rather tightly, to prevent accidental spillage. Either the flask or the accumulation of flasks would be called a "bank." The sailors, usually, were to exhausted to bother to open them to drink, so they would do the hic thing and smash the necks off of them.
HENCE: "to break the bank" became a euphemism for "to spend all ones savings in one go, simply (or presumably) to have a good time.

What do you think?