Noun
A brown paper bag.
A short presentation or seminar on a given subject, especially one given at lunchtime.
Verb
To carry one's packed lunch from home, either literally or figuratively in a brown paper bag or a lunchbox, rather than purchase it from a cafeteria or restaurant.
To consume alcohol in public from the bottle or can, while it is held concealed inside a brown paper bag, so as to avoid attention e.g. from the police.
To plant seed saved from one's own harvest, as opposed to buying new seed from a seed company.