Finally, gift bags had tiny Super Hero toys and crayons, etc. in small bags sealed with the awesome logo that was on the invitations and the thank you cards.
I had capes made of satin with Velcro closures. Each kid got to choose a brightly-colored cape and then decorate it with cut-out shapes made from sticky-back felt. This served as a fun activity and a party favor too.
The same image, minus the awesome colors, was used for coloring pages.
I purchased this image from http://www.etsy.com/shop/kottageon5th?ref=seller_info and used it for invites and thank you notes that were "Super" cute! This is a card describing the refreshments, in this case Super Hero Energy Fuel.
I have boy/girl twins who wanted a Super Hero themed-birthday party. With a dearth of girl super heroes, I asked http://www.etsy.com/shop/magneticmoods to create this image for me and I had her add "Girls are Super Heroes too!" on it.