Green’s Dictionary of Slang

(US prison) an inmate’s death in prison.

[1977		P. Hamill Flesh and Blood (1978) 32: You can do your time in Segregation or you can leave here in a pine box].
1992		Bentley & Corbett Prison Sl. 105: Pine Box Releasealso Pine Box Parole When an inmate dies in prison. (Archaic: back gate commute).
2000		(con. 1940s–60s) Décharné Straight from the Fridge Dad.

a coffin.

1964

B. Jackson Get Your Ass in the Water (1974) 64: The undertaker was the moneymaker / for every day he sold a pine box suit.

(Aus./US) a coffin.

1867		Western Democrat (Charlotte, NC) 3 Dec. 1/4: Jocular remarks [...] would be invoked by the appearance of the dead wagon [...] ‘Got on his pine overcoat at last...’.
1888		Juanita Sentinel (Mifflintown, PA) 27 June 1/5: It is a $10 wake. You see the fellow in the pine overcoat. He was one of the boys.
1896		S.F. Call 21 Jan. 2/4: Providing a cheap coffin he supposed [was] what they called in the army a ‘pine overcoat’.
1903		Bulletin (Sydney) 23 July 12/3: The wife of an eccentric old country buffer died in Maoriland a while back, and as there was nobody in the house but himself, he measured the corpse for its pine outfit and went to town.
1907		Hartford Republican (KY) 18 Jan. 3/4: The old saying of giving a man a ‘white pine overcoat,’ meaning [...] the covering provided by the undertaker.
1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1949		Monteleone Criminal Sl. (rev. edn) 177: pine overcoat A coffin.

(Aus.) a coffin.

1885		Bulletin (Sydney) 3 Oct. 10/4: Amongst the trophies presented to the festive revellers at the late Sydney Undertakers’ Picnic sports, not one, not even a little one – came from any of the medical faculty. Considering the many obligations the pine-liners confer on the pill-rollers in the way of smoothing over ‘jerried’ jobs, we consider this to be downright mean.
1887		Bulletin (Sydney) 5 Nov. 9/2: But when Alfred the Great Journalist gets a chance to describe the appearance of ‘Six Sanguinely Sweltering Suicides’ the soul of that ’Frisco man will yearn for the dark and dismal solitude of a narrow ‘pine-liner’ [...].