Green’s Dictionary of Slang

(US tramp) food (cf. mungaree n.).

1899		H.E. Hamblen Yarn of Bucko Mate 149: Pointing vehemently to his mouth and rubbing his belly, Phil said: ‘Munjy Sam! Munjy! Got any munjy?’.
1907		J. London Road 159: You hit the French country of Montreal [...] you say, ‘Mongee, madame, mongee, no spika da French,’ an’ rub your stomach an’ look hungry.
1919		W.H. Downing Digger Dialects 34: mungy (n.) (Fr., Manger) — Food; a meal.
1926		N. Klein ‘Hobo Lingo’ in AS I:12 652: Mongee — food.
1934		T. Minehan Boy and Girl Tramps of America (1976) 217: Skating on my uppers I mush talks him out of a hustle buggy ride and into mongee.
1964		(con. 1920s–40s) in J.L. Kornbluh Rebel Voices 407: Mongee – food.