Camera bag for cycling

With the changing fall colors, I am going to take a few days biking for about 200 miles through a local National Park. I plan to take my 7D, a couple of lenses, and a light tripod, but I have yet to figure out a satisfactory plan for carrying the gear. Obviously, I want it safe and secure, but I also want it easily available. I need rain protection, in case the weather goes bad. And, of course, it needs to be comfortable enough that I can still enjoy the ride.

Aside from the camera, I will be travelling fairly light. I am very fit, and the ride will be very flat, so there are no concerns about technical or performance issues on the bike. The entire ride will be on well-maintained dirt/gravel roads, so I will probably be on a mountain/off-road bike. I will not be camping.

So -- what are the suggested options?
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WLW