What should I do?
For school, I have to dress up as the word 'surfeit'. What should I dress as?

well it means  excess exg and excessive ammount of food or other object.one thing you could do is dress up as a Thanksgiving dinner for allot of people.you could thickly cover yourclothes in glitter or some other stuffyou could wear as many layers of clothes that you could weear without passing out from the heat

You could dress as a cornucopia, they have an abundance of food, which is the definition surfeit.