Green’s Dictionary of Slang

(US) to hide, to conceal.

1916		Rio Grande Rattler 6 Sept. 6: Several cautious canteen managers [...] had ‘bunked’ several hunded copies behind counters and under cracker barrels [HDAS].
1927		W. Edge Main Stem 105: ‘Say, Jack, where didja get the cigareet?’ ‘I bunk ’em ’fore I goes in de plant. I got a swell place.’.
1931		(con. 1920s) C.W. Willemse Behind The Green Lights 325: Here’s a gat [...] As soon as you leave, bunk it until you’re ready to do the job.
1949		Monteleone Criminal Sl. (rev. edn).
1950		‘Hal Ellson’ Tomboy (1952) 23: I hope the cigarettes we bunked last night don’t get wet.
1960		I. Freeman Out of the Burning (1961) 122: Where’d you bunk those guns?
1982		P. Bailey Eng. Madam 150: You manage to bunk yourself underneath so that your male organ is in no way discernible.