On pinterest I saw it made with a drawstring bag, but I found this great canvas backpack at Joan's for $4.99, then used my 40% off coupon to make it even cheaper (can't do that sort of math in my head anymore). It will make it much easier for him to tote around.
I used vellum over the top of the lightening bolt so you could see through it.
Inside is a sheet, some rope, a flashlight, some glow sticks and some clamps. All but the sheet you can find at the dollar store. I also put in some candy, because that's what any good grandma would do, right?