For the bag of the Homemade Jelly Belly Halloween Costume, I used a large, clear trash bag. I cut holes in the bottoms of the bags for our legs. Inside are obviously just balloons of different colors. I tied the bag around the neck with colorful ribbon and printed out a label from the Jelly Belly website and taped it on.
I might suggest just having the bag stop at your waist instead of cutting holes in the bottom for both legs. It was mighty time-consuming for restroom visits.
It was very inexpensive. I won the costume contest at work with this one.