Green’s Dictionary of Slang

1. (Aus.) the top gallery of a theatre, the ‘gods’.

1914		Dly Standard (Brisbane) 17 June 3/6: The star performers lived up to their high reputations, and the big audience lent their support most heartily when the famous ‘Whoop’s’ part of the programme was in progress, chocolates passed to the stalls and thrown to the ‘top shelf’ being awarded as prizes.
1922		Sun. Times (Sydney) 22 Jan. 3/1: A few of the youngest of the family climbed to a beam that stretches from one tree fork to another and perched upon it like the devotees of a theatre’s top shelf. Those that didn’t occupy ‘the gods’ played childishly around the phonograph.
1926		Sun (Sydney) 18 Mar. 17/3: There will be no ‘gods’ or ‘top shelf’ in the new theatre .

2. (Aus./N.Z.) higher-priced spirits for sale at a bar[they are thus displayed].

1981		W.D. Myers Hoops 13: ‘Hey, man, you drinking top shelf,’ I said, pointing to the Johnnie Walker. ‘I don’t like nothing cheap,’ he said .
1981		G. Johnston Fish Factory 32: Moody bugger when he’s had a session on the top shelf.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 49: Top Shelf The best, alcoholic spirits.
1999		D. Lehane Prayers for Rain 260: Oscar and Devin drank only top shelf. And they threw it back like water.