A coffin. A man who dies in prison is said to go out with a wooden habeas. He went out with a wooden habeas; i.e. his coffin.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Woodcock * Wooden SpoonNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes