What type of things will I need to pack for a school trip to Washington D.C.?

We're going to be in Washington D.C. from June 1-5. What type of clothes should I pack and what should I bring on the plane to occupy myself? How much should I bring on the plane because we are not checking bags. We get one bag to carry on with all of our stuff in it. How much money should I bring to spend on souvenirs? Thank you!