While I have not done most of the things listed above, the one I have done more than any of the others is fish. While there are many places to do this activity I'm often drawn to the same spots. On a recent trip to the confluence of the Downie and the N. Yuba river, my son did well, where I did not.
If you have children fishing with you, fish below the bridge in Downieville. If you are up for a walk for a more secluded spot, the town is a great hub with endless possibilities.