I like Jedadiah Smith Park which is actually in the very northern tip of California. It is in the middle of the Redwoods on Smith River. There are several nice beaches when you start the trip north from there. Look for tide pools, just north of Brookings at low tide. We used to spend new years at Gold Beach where the Rogue River comes into the ocean. Great beaches there. There are mail boat trips up the Rogue that are pretty cool.
Bandon is a beautiful little historical town. Just south of Charlston is Sunset Bay, which I have always thought would be a neat place to park the RV for a night. That is where the Shore Acres Botanical garden is. Very much worth the time to stroll through. There is always something in bloom there. There's Mill Indian Casino in Coos Bay that is pretty big, if you like that sort of thing. They have RV parking there. The sand dunes are north of Coos Bay/North Bend. They are good for 4-wheeling or there are riding trails. We camped at Tugman State park there. It is on an inland lake, just minutes from the ocean.
There are light houses dotting the entire Oregon Coast. Newport has the Aquariam that is wonderful. Sea Lion Caves are just north of Florence. That is a must see! Very cool. Devil's Churn is VERY cool. It is just south of Yachats (Ya-hots). You must walk down to where the water goes back in under the mountain. I think it is most spectacular at high tide. Get a tide chart so you know when high tides are in or out.
There are hundreds of neat places to stop and look around. If you make it as far as Tillimook, the cheese factory is good for a little cheese tasting. Seaside is a fun little town where there is a lot of things going on. Fun to stay there! Then you are almost to Astoria, where the Columbia meets the Pacific Ocean. Lot's of history there - Lewis and Clark, you know! Weather is always bad there.
You could easily spend two weeks just meandering your way up the Oregon Coast. I live very close to the coast and have been there many times, but haven't even remotely been to all the wonderful little places tucked in here and there. It is all two lane highway, with no passing lanes, accept maybe in some of the towns. It is slow going and some twisty turny stuff. It taks a solid two days to drive the full distance from Astoria to Brookings, and that is only stopping for lunch and potty stops!
If you make it to the top of Oregon, you can come back over to I-5 and work your way back home, stopping at some of the Miniature horse breeders dotting the way all the way back to CA.
Enjoy your trip and report back on where you went!