Any ideas for a group theme?

At my school we are having a senior field day and we have to be in Teams and come up with a team Theme. So does anybody have any creative ideas? We want something original that no one will think of. But the costumes we make have to be something that we can move around in (and school appropriate) not to expensive and something that could be done in a week. (The school didn’t give us a lot of time to prepare). And there is probably going to be around 5 to 8 people in our group