I like carolina brothers, impossible to miss and they have pie. There are a lot of options though, mostly depends on what you are looking for. I personally tend to not each much during long rides as my stomach doesn’t really like it.
Some options are Bicycles & Coffee in Purcellville, the Bike Lane in Reston, and Green Lizard (I think they all have some food, but I haven’t been recently). Also the Whole Foods and Caboose in Vienna.
Green Lizard Bike shop in Herndon for coffee & pastries on the way out, and beer on the way back, in addition to any repairs you may need. Ditto for the Bike Lane in Reston for beers and/or repairs. Both are within eyesight of the W&OD.
There are approximately 900 (slight exaggeration) breweries on or just off the W&OD. They all have clean restrooms, tasty beverages (including water refill), and some have in-house food, while others often have food trucks.
Thanks for all the replies. I ended up ignoring everyone. I stopped at South Street Under in Leesburg on the way home for lunch, mostly because I’ve been there before. I pointedly did NOT stop at any breweries, as that likely would have prevented me from making it home. But I did make it home – 103.9 miles, my first unsupported century (and only 4th overall, the other three were the Wine Country Century out in CA).