Green’s Dictionary of Slang

(UK prison) food, esp. pudding.

1906		U. Sinclair Jungle 184: They had brought him his supper, which was ‘duffers and dope’ – being hunks of dry bread on a tin plate, and coffee, called ‘dope’ because it was drugged to keep the prisoners quiet.
1925		G.H. Mullin Adventures of a Scholar Tramp 34: I received punk (bread) and a cup of mud (black coffee) or – to use the familiar hobo expression for the combination – duffer.
1936		San Quentin Bulletin in L.A. Times 6 May 7: DUFFER, bread.
1948		Mencken Amer. Lang. Supplement II 674: [...] bread, duffer or punk.