Green’s Dictionary of Slang

punk n.3

[ety. unknown]

(US) bread; thus yellow punk, bread and butter.

[UK]Contemp. Rev. Aug. 255: Bread [in America] is called punk [DA].
[US]J. London Road 159: You say, ‘Mongee, Madame, mongee, no spika da French,’ an’ [...] she gives you a slice of sow-belly an’ a chunk of dry ‘punk.’.
[US]‘A-No. 1’ From Coast to Coast with Jack London 22: Carrying the loaf of stale punk, we, too, had joined in the headlong getaway.
[US]N. Anderson Hobo 24: Someone will shout, asking if anybody wants some spuds or a piece of punk or a piece of ‘gut’ (sausage).
[US]‘Dean Stiff’ Milk and Honey Route 23: As for the Chicago, Milwaukee and St. Paul, that becomes ‘Canned Milk and Stale Punk (bread)’.
[US](con. 1914) S.J. Simonsen Soldier Bill 11: Bill learned at his first meal that ‘java’ meant coffee and ‘punk’, bread.
[US]Goldin et al. DAUL 166/2: Punk. [...] 3. (P. and hobo) Bread.
[US]Ragen & Finston World’s Toughest Prison 813: punk – Bread.
[Can](con. 1920s) O.D. Brooks Legs 2: The kid pulled a hunk of punk from a soiled brown paper bag.

In compounds

punk and gut (n.)

(US tramp) a bread and bologna/cheese sausage sandwich.

[US] ‘Jargon of the Und.’ in DN V 460: Punk and gut, Bread and bologna.
[US]‘Dean Stiff’ Milk and Honey Route 212: Punk and gut – Bread and sausage.
[US]Monteleone Criminal Sl. (rev. edn) 184: punk and gut Bread and sausage.
[US]F.O. Beck Hobohemia 21: He would all but sell his soul for punk and gut (bread and bologna) and a flop.
[US]Ragen & Finston World’s Toughest Prison 813: punk and gut – Bread and cheese.
punk and plaster (n.)

(US) bread and butter.

[US]J. Flynt Tramping with Tramps 140: His usual breakfast [...] consists of coffee, a little meat, some potatoes, and ‘punk ’n’ plaster’ (bread and butter).
[US]S.F. Call 17 July 11/2: For food he must have his trhee squares or ‘setdowns’ a day, and they must consist of meat, spuds, and ‘punk and plaster’ (bread and butter).
[US]P. & T. Casey Gay-cat 305: Punk and Plaster—bread and butter.
[US]‘Dean Stiff’ Milk and Honey Route 212: Punk and plaster route – Traveling among the Pennsylvania Dutch.
[UK]F. Jennings Tramping with Tramps 212: Punk and Plaster – bread and margarine.
[US]Goldin et al. DAUL 167/1: Punk and plaster. (P. and hobo) Bread and butter.