Green’s Dictionary of Slang

gash n.3

[printers’ jargon gash, waste matter]

(Aus.) a second helping.

[Aus]Baker Popular Dict. Aus. Sl. (2nd edn) 34: Gash, a second helping of food; any surplus or residue.
[Aus]N. Pulliam I Travelled a Lonely Land (1957) 233/1: gash – a second helping of food.