Wiktionary
brown bag
n. (context idiomatic English) A short presentation or seminar on a given subject, especially one given at lunchtime. vb. To carry one's lunch from home, as in a bag, rather than purchase it from a cafeteria or restaurant.
Usage examples of "brown bag".
Brunies bring the high-wheeled carriage to a halt and distribute a handful from the brown bag to Tulla, myself, and the other children, on which occasion he never forgot to help himself as well, even if he hadn't quite finished the vitreous remnant in his mumbling elderly mouth.
Pulling a brown bag from beneath the bungee cord on the rear fender, he craned his neck up toward his apartment.
There's a brown bag on the passenger seat with leafy stuff poking out of it.