Bags are generally made of leather and are specially tanned to produce a supple, airtight material that offers many years of maintenance free service. Several fittings are attached to the bag. All bags will need the chanter connector and the bellows connector.
When one advances to using drones and regulators, the stock cup is added to supply air to this area of the instrument. Beginners' sets very often incorporate this cup which can be blanked off pending the addition of these extras.
The neck of the bag may need to be shortened depending on the player.