Green’s Dictionary of Slang

bum n.4

[bum v.3 (4)]

a spree; also as v., to go on a spree.

[US]L.H. Bagg Four Years at Yale 43: Bum, a spree, society supper, or convivial entertainment of any sort, innocent or otherwise. Used also as a verb; whence is derived bummer, a fast young man, a fellow who bums.
[US]W.C. Gore Student Sl. in Cohen (1997) 3: bum […] 2. An excursion, the object of which is fun.
[US]E.H. Babbitt ‘College Words and Phrases’ in DN II:i 25: bum, n. A spree.

In phrases

on a/the bum

out on a spree.

[US]L.H. Bagg Four Years at Yale 527: It is seldom that a Yale man, while ‘on a bum,’ so far loses his wits as to be unable to reach his room unassisted and instances of arrest by the police of drunken students are almost unheard of.
[US]M. Thompson Hoosier Mosaics 117: I got onto a bum in Jacksonville and spent all my money and everything else but my very oldest suit o’ clothes and my pistol.
[US]E. Custer Boots And Saddles 193: I intend to celebrate their return by going on a tremendous ‘bum’.
[US]J. Maitland Amer. Sl. Dict. 52: On the bum, on a drunk.