Green’s Dictionary of Slang

1. loose-fitting ‘boxer short’ style of swimming trunks.

1962		Aus. Women’s Weekly 24 Oct. (Supplement) 3/1: Baggies, baggy pants worn over swimsuits when riding a surfboard .
1965		N.Y. Times 10 Aug. 31: Among their boyfriends ‘baggys’ (loose-fitting swim trunks) were de rigueur.
1971		Studies in Eng. (Univ. Cape Town) Feb. 29: Brilliant is of fairly wide application, e.g., a brilliant board, a brilliant ride, a brilliant pair of baggies [OED].
1981		W. Boyd Good Man in Africa 101: [He] eased up his swimming shorts, a pair of psychedelically patterned surfin’ baggies imported from the USA.
2000		R.G. Barrett Leaving Bondi (2013) [ebook] [F]ive young hoods wearing baggies and floppy beanies.

2. (also baggy-foot pants) loose-fitting baggy trousers.

1967–8		Baker et al. CUSS 76: Baggies Pants.
1989		C. Hyatt When Me Was A Boy 36: Yuh mother wi ’low yuh fi wear yuh new baggy-foot pants an sailor-boy shirt.
1991		R. Doyle Van (1998) 524: They’re not flares, righ’! They’re baggies.
1995		(con. 1985–90) P. Bourjois In Search of Respect 159: I dressed good, like in nice baggies, and fancy shoes.
2000		T. Blacker Kill Your Darlings 65: You changed your style. No more baggies now. Certainly no more baseball caps turned the wrong way round.
2004		(con. 1960s-70s) T. Taylor Top Fellas 48/2: Baggies were high waisted and very flared, so flared that they’d cover the whole of your shoe.