The simplest version of the jug is a tall cylinder with a pouring spout. But with the jug you can really go in any direction. A convex belly, a sloping wall or a whimsical shape…. as long as the jug can pour, you’ll be fine.
And you also have options with the spout. You can shape it by gently stretching the wall, you can cut out a spout from the wall, or you can cut a hole in the wall and attach a separately shaped spout. Plenty of possiblities!