Also, a great send-off gift is a pre-paid/loaded Metro card (you can decide how much to start off with, and then more money can be added later). Once you get to DC, all the museums are free and he should def take advantage of this on weekends.
http://travel.usnews.com/Washington_DC/things_to_do/free/
https://washington.org/visit-dc/where-to-get-the-best-instagram-in-washington-dc
https://washington.org/100-free-and-almost-free-things-do-dc