Park hoppers are nice, but not essential as long as you can go to both parks.
Here are the rides I always consider must dos at
Disneyland:
Space Mountain (currently Hyperspace Mountain)
Buzz Lightyear
Star Tours
Matterhorn (it’s painful but it’s a classic)
Peter Pan
Alice in Wonderland
It’s a Small World
Thunder Mountain Railroad
Indiana Jones
Pirates of the Caribbean
Haunted Mansion
Splash Mountain
And at California Adventure:
Guardians of the Galaxy
Soarin’
Grizzly River Run
Radiator Springs Racers
Incredicoaster
Toy Story Mania
There are other rides that are great too but these are the must dos.
Use Fastpass and single rider. These rides have Fastpass:
Space Mountain (Single Rider line works amazing so I hardly ever get Fastpass anymore)
Buzz Lightyear (Fastpass doesn’t run out quickly but is generally worth getting one when others are out)
Star Tours (I highly recommend Fastpass)
Matterhorn (Single Rider works great)
It’s a Small World (you probably won’t need it but maybe you will)
Roger Rabbit (I honestly have no idea if this is a good idea, because I don’t ever ride this)
Thunder Mountain Railroad (Fastpass is great and they don’t run out super quickly)
Indiana Jones (Single Rider is terrible. Use Fastpass.)
Haunted Mansion (Fastpass is fine, but you might not need it)
Splash Mountain (get it for hot times of the day. Single rider works well sometimes but don’t rely on it)
And in California Adventure:
Guardians of the Galaxy (I highly recommend Fastpass)
Soarin’ (I highly recommend Fastpass)
Radiator Springs Racers (Single Rider is great. If you decide to get Fastpass get them early)
Grizzly River Run (Single Rider works if you’re ok sitting in the raft with other groups. Some find this awkward)
Incredicoaster (Single Rider works sometimes but on busier days I recommend Fastpass)
Toy Story Mania (I highly recommend Fastpass)
Goofy’s Sky School (I never ride this. Single rider is an option.)
I highly recommend getting Maxpass. It is $15 per person per day. You can get more than with regular Fastpass and if someone cancels, you can get their Fastpass.