If you are a disciplined packer you can buy large capaticy in case you might need it later without overpacking. But that's a big "if" for some people. As Bruce Gordon told me when I was looking for my first set up, a lot of people tend to fill up all the space they have and end up with too much. That was certainly true in a couple of instances on my first trip, which was a x-country trip. One woman started out with a blow dryer and a Watchman TV, among other creature comforts. At least three people mailed stuff home on the third day.

I ended up going with a paretty large capacity set of racks and panniers from Robert Beckman because I wanted to carry a lot of film camera equipment. But even then I did not max out the rack and bag space because I was disciplined about the clothing, etc., that I took. When I had to replace the Beckman stuff I went with Nitto Big racks and Ortlieb Bike and Sport Packers Plus panniers. They also afford me a lot of capacity, but I never fill them. And I have left over space to easily carry groceries and a sixer if I camp a ways from a food source.