To take one's lunch to the office, or one's liquor to a club or restaurant, in a paper bag : for brown-bagging booze at places that allow this practice/ brown-bagging it for lunch (1960s+)
[second sense fr the notion that such a person should wear a bag over the head to hide the face]
A person who brings his or her own supplies, as in The architects of the new office designed a space for brown baggers to eat lunch. The term originated in the 1930s in Britain for very serious students who carried their books about with them in brown briefcases or bags. That usage crossed the Atlantic within a few decades. However, in America from the 1960s on, it has primarily been used for persons who brought their own liquor in a brown paper bag, either legitimately or surreptitiously, to a public place or restaurant not licensed to sell it, or for those who took their lunch to work.