A dark lanthorn: an allusion to Guy Faux, the principal actor in the gunpowder plot. Stow the guy: conceal the lanthorn.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Gutting a Quart Pot * GuzzleNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes