Green’s Dictionary of Slang

1. (US campus) to go out on a spree.

1860		implied in bumming n. (1)
1871		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.
1936		W.W. Williams Quiet Lodger of Irving Place 239: ‘I'm going to have you meet a couple of celebrities tonight [...] we'll all have dinner together, then go bumming and see some of the town ’.
1974		(con. late 1940s) E. Thompson Tattoo (1977) 576: We just came around to see [...] if maybe you’d like to go out bummin with us a little. You know, like old times.

2. to play truant.

1927		F.M. Thrasher Gang 169: The gang bummed school two weeks to take a camping trip to Fox Lake. We did not have no money; we must think up a scheme to get some.
1932		(con. 1910s) J.T. Farrell Young Lonigan in Studs Lonigan (1936) 145: He bummed from school and met Weary and Paulie.
1936		J.T. Farrell World I Never Made 216: I’m not going up to Miss Timmins and say you been bummin’ from school.