Long, long time ago on a block not too far away (depending on where you live in the TC) was a dairy. There were no cows to my knowledge, but there where milk trucks and milk. I know this from the 1924 map here and from a few newspaper reports of people getting run over by milk trucks. Which is bad.
Anyway, a few years back I discovered that you could buy these bits of Truxtonia on Ebay. You still can. I found three today by plugging in the name of a dairy that was here "Fairfax Dairy" another name, as well as Alderney Green Meadow and plain old Green Meadow. Some have the address embossed on the bottle and some like this one, do. They also range a lot in price, which I guess these things matter more to collectors, but they go from under $20 to somewhere around $60 for pint and half-pints.
I'm sure there are other bits of TC history out there. The problem is finding what are the right search terms.
Haven't found too much else, not that I'm looking that hard but I have found these nearby gems:
Wonder Bread Wrapper- 23?? Georgia Ave NW
Antique Tin Automobile Gas Station Can- One of the several addresses is Bloomingdale Florida and Q St NW
Lehman's Tire Shop- Photo, no clue where this is in DC. Could look it up, but I'm lazy.
Photo-Piggly Wiggly Trucks, 1924- I'm guessing near the Post Office Pavillion?
Mom's Mabley LP- Recorded at two places, one being the Howard Theater.