Ah, the timeless flour sack. After looking for a simple/appealing sack rig for animation practice, I decided to create my own. And to give back to the animation community, I'm offering it here free for non-commercial uses. If you enjoy using it, feel free to tip me what it's worth to you, or just send some good vibes my way!
See it in action here: https://vimeo.com/72566266
[Created for Maya 2013 and up.]
There is a wide range of flexibility to the rig, so play around with the controls to achieve the desired pose. Many of the controls can be translated and scaled non-uniformly for extra control.
Posing Tip: I recommend thinking of the yellow cylinder controls (Top_Control and Bottom_Control) as the primary first-pass pose controls, and pose them first. The shoulder controls have an attribute that sets whether they follow the hierarchy, or are free to stick to the world. You may want to change this, depending on your scene.
Check out my other rigs here: https://gumroad.com/joedanimation