Last year, I went to
Walmart and bought the cheap plastic type ponchos for like .88 cents. Just slipped one into my back pocket and had it if I needed it. When I was done with it, I threw it away and didn't sweat it. I think that I bought 15 or so last year and have most of them left to take with us again this year.
They are not the best quality, but they definitely do the job.
The Disney ones are nice and probably worth the price, but it isn't worth the hassle of drying to prevent mildew IMO