"No wuckas" is an abbreviation for the term "no wucken forries". "Wucken forries" is a spoonerism of the term "fucken worries". In any form this term is usually followed by the address "mate".
A: "hey mate do you have a spare smoke by any chance? "
B: "yeah sure, here you go mate"
A: "thanks heaps, mate"
B: "no wuckas, mate"