Hallow-Green party costume

I'm going to a halloween party at a club and its sponsored by the local South Florida Chapter of the US Green Building Council, so everything is GREEN. Organic treats, organic vodka, green goodie bags, and contests for "green" costumes.
So, I'm dressing up as a re-usable grocery bag.
I'm making my costume.
Here's how I'm doing it: I'm getting a cheap canvas dropcloth from home depot and sewing it to look like a human-sized bag with arm holes and leg holes (gotta walk!) I may velcro the back so I can get out to pee!
I have an old small bag that has a big hole in it so I cut off the handles and I'm sewing those onto the costume.
I downloaded a chasing arrows recycling symbol and I'm going to print it on iron-on paper and iron it onto the costume.
I may also get a little wire to give the "bag" some shape.

I think it will be evident what I am, but I may tape some food boxes into it, like an empty box from an Amy's frozen meal (organic!). Any other ideas on how to nail this costume so I can win some green($)?

You can use my idea if you want, because I don't think any of you are going to this party, so its cool. :) But I am seeking some good tips.

Thanks veggies!
Kristen