I bought this Electro luminescent (EL) wire disk off eBay as the 'Tron Blue' colour was just begging to be made into a little backpack style bag that could be worn like the ID disks from the film TRON: Legacy 
Step 1: Construction
I cut two disks of heavy black cotton fabric, using tailors chalk to mark 10" diam. circles.
I used 2 black plastic side-release clips on 1" black polyester webbing for adjustable strapping, one for each shoulder.
There's a zip along the top arc of the bag, this isn't just a costume prop, it functions as a bag.
The disk sits on the outside of the bag held in place by a clear PVC disk to splash proof everything. The wires from the disk go back into the bag through a buttonhole opening.
On the inside of the bag, a black elastic keeper has been sewn into the bottom arc seam of the bag to hold the battery pack. It takes 2 x AA and you'll get more than one evening out on a fresh set of batteries.
There's Constant ON mode, plus 3 speeds of Blinky to choose from.