Green’s Dictionary of Slang

1. (Aus.) to carry someone on one’s bicycle cross-bar.

1959

Baker Drum.

2. (also bonk) to travel without a fare, to get in (e.g. to a cinema) without a ticket.

1982		E. Mac Thomáis Janey Mack, Me Shirt is Black 121: We tried to bunk into the barracks as the gates opened to let out the horses.
1988		R. Doyle Commitments 106: EASY TO BONK YOUR FARE.
1999		Observer Mag. 15 Aug. 13: I still insisted we bunk the fare.
2004		N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 37: Nicking milk from door-steps was natural to us, like bunking on the tube.