The container you refer to can be any bag or box.
Open the broker window and click the sell tab. In the top left corner there is a box with 6 smaller boxes in. DEpendant on the size of house you have you can have 1 to six of these slots available. Just put a bag or box into one of these slots, then drag and drop the things you wish to sell into the bag. Set a price you wish to sell the item for and away you go .