smoko comes from smoke break. In this context bikkies (biccies in British slang) would usualy be the type of biscuits merkins refer to as crackers.
Chocolate Chip cookies and Swiss works, though, just sayin'......
arvo from afternoon I think because some people (not speculating who *coughcockneycriminalsanduppercrustgovernorsofprisoncoloniescough*) (used to) pronounce afternoon with a longer "a" sound ........and it is mandatory for all aussie slang to end in "o".