Any type of alcohol (especially beer and liquor). This term is typically used in social contexts--but definitely not at a highbrow cocktail party. Use this term when you don't want to be blatant about your alcohol consumption (in front of parents, grown-ups, etc) or when you just want to sound fratty.
Teenage kid #1: Hey, dude, are we set for the party tonight?
Kid #2: Yeah, don't worry. My big brother already picked up the liquid assets for us.
Kid #1: Sweet. Thanks.