Busboys and Poets (4 blocks west at 5th & K) - A DC Institution. You will not be forgiven if you do not make at least one pilgrimage here.
Maddy’s Taproom (4 blocks east at 13th & L) - Good beer selection.
RFD Washington (4 blocks south at 7th & H) - Large bottled beer selection, good draft beer selection (food ain't that great).
Churchkey (6 blocks northeast at 14th & Rhode Island) - Officially, one of the best beer rooms in the US.
Stan's Restaurant (7 blocks east at L & Vermont) - Downstairs, casual. very strong drinks. Supposedly good wings (I'm a vegetarian, so I hold no opinion)
Daikaya - Ramen - Izakaya (7 blocks Southwest at 6th & G) - Upstairs bar can be easier to get into sometimes. It's a popular place.
Teaism, Penn Quarter (8 blocks south at 8th & G) - Great snack place mid-way to the national Mall. Large downstairs dining area. great place to have some tea, a snack, and catch up on conference planning.
There are, of course, lots of other places within a short walk. I recommend 14th street in general. 9th street has some good stuff, especially as you get closer to U, but it's a little sketchy of a walk.