-- Last Updated: May-31-11 11:58 PM EST --
has a website for the upper sac. There are still some stretches of undeveloped public lands along the river. BLM has the Sacramento River Bend area of public land, with a primitive boat-in only campsite at Massacre Flat, below Jellys Ferry. At the Red Bluff Diversion dam there is a developed campground with all the amenities. Further downstream is the chain of State and National Wildlife Refuges, some of which allow camping on the sandbars (but in late summer no campfires). Woodson Bridge State Rec Area has a paddle in campsite.
So the short answer is yes, it is possible, but most of the shore is either steep banks, or mega-thick riparian vegetation that does not yield a good campsite. Many of the suitable spots for camping are already designated as campsites.