GH gives away free slices and also sells cookies and other baked goods. So still worth a stop IMO (Sundays & Mondays excluded – closed). They have another store in Vienna a block south of the W&OD (just past Bikes @ Vienna).
DQ is OK for quick snacks, Breeze is a sit-down place with decent food (primarily Greek & Italian themes). Not sure what the other place is. There are more restaurants around the corner on Elden St, and a bunch more (mostly along Elden) in either direction from the bike trail crossing. Mix of sit-down and take out and a few fast food eateries.
Your other convenient venue for food near the W&OD is Reston Town Center – several places are take-out and would be cyclist-friendly.
Steve