"Baggies" is the name of a brand of sealable food storage bags manufactured by the Pactiv Corporation. So referring to plastic storage bags as "baggies" is similar to referring to how Americans call tissues "Kleenexes" -- I've personally never seen/heard an Australian refer to them as baggies, only from Americans.
Mind you, how many Australians call adhesive bandages "Band Aids" (even if it's not the Johnson & Johnson's brand)? The use brand names as synonyms for the actual product isn't quite as culturally ingrained here.