First, if camping in state parks then hiker-biker sites are first come, most everyone served. If you want a conventional site, then you'll need reservations. The tough part is connecting the dots if you choose to do an inland loop for camping sites.
Suggested Loop route: SF to Vallejo by Ferry, ride to Bothe-Napa SP, north of St. Helena. B-N SP has HB sites and a lot of good eats along the way. Here it gets tough - do you go to Clear Lake as Jamawani suggests or do you start thinking about the coast. Clear Lake is a reasonable destination but it is hot in July, Worse, Getting to Clear Lake is a bitch. You don't want to take 29 unless you have to - it is narrow and has relatively heavy traffic. 29 twists and turns as it climbs the shoulder of Mt. St. Helena and has no shoulder - It's highly not recommended. There is an alternate - further north of Calistoga is Ida Clayton. Great scenic road but just a stinker of a climb for several miles. Over the county line (to Lake County) the road turns to powdery dirt for the descent into Lake County on Western Mine Road. Once past that you rejoin CA 29 for the ride to Middletown. From there you would continue on 29 towards Kelseyville and Lakeport. There is Boggs Mtn State Forest, but I'm not sure of the camping opportunities. And this to me would be the problem with this route, is the limited number of camping opportunities in this area. Personally, I don't care much for Lake County and would suggest you avoid it.
So if you don't go to Clear Lake, then you could continue north of Calistoga on CA 128 towards Geyserville. Above Geyserville there is a KOA where you could probably camp. From this location you would track back through Dry Creek Valley to head towards the Russian River. Alternatively you could cut through Healdsburg (great eats and lodging) and work towards the Russian River (Westside Road, River Road). There's a campground near Korbel Winery, think it's called School House (private) that would be worth a shot. The gist is that you would start to work through the Alexander Valley towards the Russian River to head out to the ocean. Road traffic is moderate and the roads have decent shoulders. If you consider this area and route do not give any thought to going towards Warm Springs Dam and trying to reach the coast by way of Skaggs Springs - Stewarts Point Road. Unless you like hot temperatures, extreme grades (12-18%) and no services - including water - zip, nada zilch. It's 40 miles of the most beautiful and rugged terrain but a nightmare if you are fully loaded and just returning to touring. Stick to working towards River Road and CA 116 on back roads to reach the coast.
Presuming you stick to this itinerary, CA 116 will take you to the coast. A short run down to Bodega Bay will take you to Bodega Dunes SP with its teensy-weensy HB site. Within easy reach of town for supplies. Options include riding out to Bodega Head and various hikes. From Bodega Bay traveling south takes you to SP Taylor SP with more HB sites. There's also a great B&B in Olema, The Bear Valley Inn, run by a former LAB board member - you get a discount if you arrive by bike. A good spot to hole up for a day or two and ride out to Pt. Reyes and back - 40 miles or so.
Presuming you've stuck this route out, you're now 1 day away from returning to SF. So there's a good 5-6 days of riding in some fabulous territory.
If you want to do the coastal O&B then it's just those last few days in reverse order going north before you turn south. Hope this helps.