We are all aware of the Federal workers who have been furloughed and may not be given back pay when this nonsense ends, but there are other people suffering because of the shutdown who will never regain their lost revenues.
Public Transportation
Metro is the main provider of public transportation in these parts, both the buses and the subway. At rush hour there are about 200,000 riders and about 40% of those are Federal employees. There are a lot of nearly empty buses and subway cars running. Metro has been losing riders lately and there are lots of repairs and upgrades that desperately need to be made. This is not helping
Food Merchants
All those office building are usually filled with hungry Federal workers and there are lots of people waiting to sell them food. There are corner shops that are only open for breakfast and lunch (downtown is pretty much a ghost town after 5:00pm) and food trucks selling everything from half-smokes to lobster rolls. A lot of those offices are nearly empty and there is no one standing in line to grab a quick lunch. A lot of those restaurants and food trucks don't have much cash in reserve.
Souvenir Merchants
Tourists have figured out that with all the Smithsonian museums closed there isn't much reason to visit. All those guys selling "Proud to be an Undercover C.I.A. Agent" aren't selling much.
Tour Guides
OK, technically the tours that take you around the city are still operating, but nobody is coming to DC just to ride a Segway. I'm sure their business is way down.
And this isn't just happening in DC. ALL the National Parks are closed. These parks are mostly in wilderness areas. I'm sure the locals who run the motels and restaurants and convenience stores will complain about idiot tourists, but they rely on those tourists for income. Most major cities have large Federal employee presence. It may not affect the city as a whole, but those coffee shops right next to the local Social Security office building are probably hurting. And even if the shutdown ends tomorrow none of these people will ever get that money back. That's money that's not going in the local economy, not being used to build a bigger or better business.
Federal employees will be fine, even if the Republicans don't make up the back pay, but some of these businesses may never recover.