L.H.
capes!
I did this for my son's party. For their favor, I made capes. I did a really simple design that was a rectangle with a folded over pocket at the top. I used a ribbon to do the neck with velcro. It is kind of like a one sided pillowcase dress. They cost about $1 to do.
The kids were hillarious!!! They were running around making flying noises and saying "to the rescue!". They made GREAT pictures too.
If time is an issue for you and cost is not, you should check etsy.com They have capes there.
L.