I'm going on a trip to Washington DC. What should I wear?

Your honor society outfit would be perfect. However instead of the denim jacket pair it with your brown blazer OR you can pair it with a pink or brown cardigan. Heels will not be neccessary at all because you will be walking a lot. So your brown flats will do just fine. The weather here is starting to peak into Spring weather some days so pants/jeans, long sleeves, and a sturdy trench coat would be fine, but dont forget a scarf, gloves, and hat because sometimes its tricky. Have a great tour, you'll love it!