Here is the ride I would do. Pretty hilly, but gorgeous ride.
Head east on Sir Francis Drake to San Geronimo.
Left on Nicasio Valley Road at Golf Course.
Ride over Golf Course Hill into, and then through, Nicasio
Right on Petaluma-Pt. Reyes Road
Climb Hill to Cheese Factory, then slightly past
Turn left on Hicks Valley/Wilson Hill Road
Left on Petaluma/Marshall Road
Over Marshall Wall, then down to Hwy 1
Left on Hwy 1. Ride along Tomales Bay to Pt. Reyes Station
Get an almond croissant at the Bovine Bakery and refill bottles
South on Hwy 1 out of town, then right turn on Sir Francis Drake towards Lighthouse
Ride SFD through Inverness and all the way to the end at the lighthouse.
Retrace your route back towards Inverness, then turn right on Bear Valley Rd.
Rejoin Hwy 1 in Olema, then a quick left on Sir Francis Drake
Short climb over Olema Hill.
At Platform Bridge Road (bottom of the hill), look for the bike path. You can ride a short dirt section on the right side of the road, or go under the road from the opposite side where P.Bridge hits SFD. (I would avoid SFD through this section. It sucks).
Ride the bike path back to your campsite.