I bought a Blackburn saddle bag today to fit on top of my luggage rack. I've already got panniers, but there may not be enough space for our Lands End trip. I'm quite happy to cycle with a heavy load, as we'll only be cycling 50 miles a day, and we are both happy to go at a slow pace. Here's a photo. The saddle bag will also be useful on day trips when I don't need to take more than waterproofs, snacks and a flask.