Ulysses Unzueta is a student at Animation Mentor, and was a student of mine. He needed the bag rigged for his scene, so I helped him out. After studying his blocked shot I decided it was best to treat the bag as though it were a spine rig. Only thing missing is FK joint chain for the spine. I’ll add it later. Here is Uly’s work in the refining stage.
Bag Rig
In this shot, the bag and the rig for the bag is my contribution. The character, Stewie, is a product of the Animation Mentor online school.
You all can have the bag, too. Cheers. 
Download it.
Here’s a demo on the rig.
Bag Rig Demo
Tags: digital arts, Maya, rigging