I live in the Six Rivers region of CA. Can't think of more than a couple of places where you could camp along the river where you could actually use a raft.

Van Duzen, too low generally

Sacramento ?

Trinity some camping nearby, along Hwy299.

Smith some along the way.

Eel depending on which fork there are some opportunities. Flow is pretty poor usually

Klamath dammed, lots of drift boats not sure about any camping along the way

Mattole no flow, shallow

Rest of CA? anything?

CA is a huge state. I don't see much opportunity for packrafts though. Lakes we got.

So where does all this rafting go on, Idaho and Montana?

All main forks of the American River and connected tributaries (e.g. silver fork, rubicon river, caples creek)have excelent opportunities (class 2-5, plus National Forest land with trails and camp where you want.) Generally look at the Tahoe and Eldorado NF between 3,000 - 6,000 ft. elev.

Smith should be good if my ~decade old memory serves. That river that runs through Redwoods and comes out at Orick should be too. Gotta be some creeks in the Marbles and Trinitys that are at least seasonally good.

I work in Folsom and have taken mine on the nearby S. Fork American several times. The stretch from Chili Bar to past Greenwood Creek (Hwy 49), although not wilderness, is a lot of fun in a packraft.
Someone recently posted either here or packrafting.org about a nice trip he did with his daughter in Redwood Nat. Park (I believe the one Dave is referring to). It didn't sound very long, though they did have a nice campsite. I have often stared at my map of the Klammath River region looking for possible hike/raft routes along 299, but like you said, it's not so clear. I thought of maybe using Trees of Heaven campground as a base for exploring.
cacreeks.com has a list of runs by difficulty with info about each.
Recommended Runs
As far as ultimate California packrafting adventures go, it's not NorCal but one can't help but admire Wyatt Roscoe's Headwaters of the Kern trip report from last year. I have hiked along that river a few times and it's really beautiful.
Headwaters of the Kern

Let's get together and do some packrafting some time, Ken!

Cache Creek when they let out water in the summer?

http://www.blm.gov/ca/st/en/fo/redding/recreationmain/reddingrecreationtehama.html

The map on that website shows BLM land all the way to Battle Creek, which, in addition to the Sac, can be boated. The terrain is mostly wide open for cross country hiking. Considering where it is located, the area has a remote feel.

Edited by blatargh on 02/12/2013 22:30:13 MST.

So frustrating to see the Eel flow upstream when the tide comes in. OK so a few more places to look into. Although fun I'm not necessarily looking for whitewater I like the big group boats for that. Drowned once. Pass on doing that again. Tend to be more cautious in/on the water.

Edited by kthompson on 02/12/2013 22:37:29 MST.

Sacramento River and the lower section of Battle Creek I mentioned are class I and II.