Green’s Dictionary of Slang

1. (US drugs) the act of frequenting an opium den, too poor to buy one’s own drugs but in the hope that someone else will offer a treat or simply to inhale the airborne fumes.

1935		A.J. Pollock Und. Speaks n.p.: Bunk habit, one who enjoys watching opium smokers smoke but is not an addict.
1936		D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 1 in AS XI:2 119/1: bunk yen. The tendency shown by a down-and-out addict to hang around a den even though he has no money for a lay. Restricted to opium addicts.
1969		R.R. Lingeman Drugs from A to Z (1970) 53: bunk habit [...] The practice of lying around in a place where others are smoking opium for the purpose of inhaling the fumes though not smoking oneself.

2. (US drugs) the desire to sleep excessively, resulting from one’s addiction to narcotics.

1946		Mezzrow & Wolfe Really the Blues 246: Mike’s dog [...] had a bunk habit too, so he was evil in the morning.
1949		Monteleone Criminal Sl. (rev. edn).
1958		E. Gilbert Vice Trap 88: He had the bunk habit of junkies.

3. (US drugs) a narcotics addiction [poss. misinterpretation].

1938		D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 2 in AS XIII:3 182/1: bunk-habit. [...] 2. An opium habit.
1959		J.E. Schmidt Narcotics Lingo and Lore 22: Bunk habit – The narcotic habit, especially addiction to opium.