For food, you could try NuVegan Cafe. They serve vegan soul food and, since they are all-vegan, there is no concern about pork and everything should be halal. Plus, the food is delicious.

I don't know which museums you are planning to visit, but I highly recommend the Smithsonian American Art Museum. It is a few blocks away from the National Mall and the majority of the museums but it is a wonderful museum with many gorgeous and fascinating pieces.

If you are going to the Museum of the American Indian, they have a great cafe downstairs that serves Indigenous foods from all over the Americas.

Since I saw you mention in another comment that you will be visiting in mid-October, I do recommend bringing jackets and clothes for cooler weather, wind, and rain, as well as clothes you would be comfortable in if the weather is moderate (24 degrees C or a little warmer isn't unheard of at this time of year).

I hope you have a wonderful trip!