Green’s Dictionary of Slang

(Aus.) a lift on the crossbar of a bicycle.

1934		Bulletin (Sydney) 5 Sept. 20/2: The fortunate Melbourne schoolkid with a bike [...] is asked by his cobbers for a ‘dink’.
1993		Aus. Word Map 🌐 ‘To “double-dink” was an verb, as in, “They're double-dinking!” “Dink” was the noun, as in, “Can you give us a dink?” or “I can give you a dink.” [...] In either case, the pasenger sat on the saddle (or luggage rack) not the bar, leaving the peddler to stand’.