Guess what this is?

City Beach (Perth, Australia)

So... any guesses as to what this is? I saw it rolling along the beach (Perth is very windy, haha). I'll buy dinner for the first person who tells me what it is.... or at least guesses what I think it is.
Just leave your guesses in the comment box. B, you're disqualified from guessing since I told you already. No annonymous guesses blogstalkers, unless you want to donate your free meal to me =)