A few people who are contemplating riding either the GAP or C&O (or both) have asked about what kind of gear they need. Here is a brief rundown on what I had and recommendations.
The Bike: four years ago I ventured into the world of “gravel” bikes with the purchase of a Specialized Sequoia. Sometimes these bikes are also called “adventure” bikes. They are “sort of” like road bikes adapted for riding gravel/dirt/off-road, with larger tires and disc brakes. I do indeed ride mine on lots of gravel roads (I live in farming country) and I also use it around town for errands, including groceries. It can also handle “light” touring, which I suppose refers to shorter trips. I bought mine with the ride along the C&O and GAP (Great Allegheny Passage) in mind. It was perfect for the trip. It has a steel frame, carbon-fiber fork, hydraulic disc brakes, 42mm tubeless tires and wide handlebars.
Disc brakes: I am now totally sold on them. Besides being more reliable in the rain, they help you stop easier, with less effort.
I ride larger, tubeless tires, a pair of 42mm Specialized “2 Bliss.” These smooth out some of the roughest parts of the road and give good traction. I have ridden the entire GAP multiple other times on road bike tires (25mm) but I recommend larger tires overall and they are essential on the C&O towpath.
The Sequoia has a set of wide, drop-handlebars. They even have a “flare” to them. All of this provides more stability on uneven roads.
I ride Shimano two-sided pedals. One side as an SPD clip on it and the other side is flat. That means I can ride with either cycling shoes or street shoes. In my case, I rode at least halfway in Chaco sandals. Not having to unclip every time I wanted to stop (and since I was doing a lot of photography and looking at historical markers) that was frequent. When I hike I like to do it in sandals, when possible (see this post) and on hot days they are very cool.
I carried all my gear in a pair of Ortlieb “classic” saddle bags, waterproof, with a 40-liter capacity. I had some light rain, and lots of puddles, but they kept everything nice and dry. Mine are yellow, for visibility, because you really can’t have too much visibility on a bike.
Overall, I packed too much. When I walked the 500-miles Camino de Santiago a few years ago, I carried only 15 pounds. I knew that I could carry more on a bike, so I got a bit lazy. Since this trip was research for a book, I carried four books along. I took too much clothing. I had to take some food, so that was non-negotiable, as were the bike tools. All of it came to about 35+ pounds and when I do it again (and I plan to, next spring) I’ll carry less. Unless I’m planning on camping, in which case I may carry more!