A petty cook’s shop, where there is no credit given, but what is had must be paid DOWN WITH THE READY SLAP-BANG, i.e. immediately. This is a common appellation for a night cellar frequented by thieves, and sometimes for a stage coach or caravan.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Slang-1 * SlapdashNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes