I am not a real fan of ultralight headsets - I like having single muff head vices during a show. That said, when I am preshow, I usually wear a modified earwig (I worked for a few months at a University, and had the electronics department modify my 2 way radio earwig to take both clearcom/tecpro input and my 2 way at the same time).
That said - Beltpack.com really only make one ultralight, and it is a headband type - if you don't mind that, it is a good little headset. I can't stand headband headsets, so I loath it. Their other headsets are great though.
My best advice would be don't skimp on it (cost wise) and take good care of it. I used to own my own set of head clamps, I did skimp on them, and even though I took excelent care of them, they recently died.
As for the silver lunchbox - great idea. What I would suggest is talking to costume and seeing if someone there is willing to make you a headphone case (buy some leather and a good quality zip)