Deck Bag
I have a deck bag which also serves as a water bottle holder and map case. I leave the digital camera on a tether in the bag (or slide it under the bag) and use it as I need it. Sometimes I just snap the tether to my PDF and leave the camera in my lap as it is in a waterproof case.
Sealine Dry Bag
I have a mid-sized (model 10?) sealine dry bag, attached with a short piece of bungee to my seat. I put the camera in there (an all manual SLR from 1975) and use it when I need it.