We did this last December and it was fabulous. The beautiful US Botanic Garden gets all decorated for the holidays AND puts up an incredible working model train display in a side room. They are doing this every Tuesday and Thursday evening so I strongly encourage you to visit (on this night or others). It is one of the nicest holiday venues in the area. Here's their website. It's free, Metro is close, parking is easy, and the place is incredibly decorated and under-visited.
On this night, we'll enjoy the choral performers Capital Accord Chorus - so get your pipes warmed up! I don't think they sell any food or drinks, but you can bring something in. We will walk across the Mall to Teaism afterwards for a bite to eat. That's a really nice walk to make this time of year; we'll see the Capital Christmas Tree and other holiday highlights.