For any guests who aren't from SoCal, Disneyland is a must! Even visiting Downtown Disney for the afternoon is a nice place to walk around and eat.
If you're looking for a place to go shopping, the Irvine Spectrum Center is a great outdoor mall option.
Knotts Berry Farm is another good amusement park option in Orange County. It's a great place if you're looking for roller coasters.
We definitely recommend visiting the San Clemente Pier, or any beach in Orange County!