This form is widely but wrongly known as a "costrel" because its primary use was not for carrying liquor but for drinking it, in the tavern or in the fields. It is, then, a bottle (bottel or bottell in its day), the drinking vessel of choice for laborers and artisans. Now really rare: bottells could not be coated inside with tar like blackjacks so the leather dried and began leaking comparatively quickly. This one has a wonderfully aged surface - a joy to see and to handle. (Final image: bottle from the Mary Rose, sunk 1545)
Details and more photos.