Blue athletics day costume?

Tomorrow is my high school's annual athletics day, and practically everyone wears a costume. My house colour is blue, so my outfit has to be blue. I don't know what to dress up as. Could anyone please give me some ideas? I don't want to spend heaps of money and it can't take hours and hours to make. I need to be able to get what I need at the mall. By the way, I'm not a serious athlete so it doesn't matter if it's hard to compete in or whatever. Also, it needs to be transportable because we have to catch a bus to the event. Thanks :)