Is there anything more iconic than a summer day in Southern California? With perfect temperatures and a laid back culture, California easily tops my list of favorite summer getaways.

When to Go
Any time of the year is perfect for Southern California. The weather is great year around. Most people will head there for their summer vacation and usually end up visiting between June and August.
Getting There
I recommend splitting your time between San Diego and Los Angeles. There are a couple of options for figuring out the flight situation. You can either do a round-trip to San Diego or LAX airport, or one-way to one of them and one-way return flight home from the other. It's best to check out the cost for each of these options and decide what works best.
Where to Stay
We did 3 nights in San Diego, 1 night in Huntington Beach, and 3 nights in Los Angeles. While in San Diego, Airbnb or hotels are fine since it's a less expensive city. I would either plan to stay in downtown San Diego or Pacific Beach area depending on what your plans are. In LA, I would recommend Airbnb to avoid high hotel costs. We stayed at an Airbnb in West Hollywood neighborhood since it was close to many of the places we planned on going. Just make sure they have free parking available if you're keeping the rental car with you.
Packing
Packing for SoCal in the summer is a breeze. I used my handy Osprey backpack and just packed up the essentials; it's summer you all you need is a swimsuit, a few dresses, and a pair of jeans and a sweater. It gets a little chilly at night, so don't forget a light sweater/jacket.
Transportation
It makes sense to get a rental car so you can drive along the Pacific Highway and go beach-hopping. The two cities are not far from each other (about 2 hours) and there are buses/train options if you can't drive, but you'll be pretty limited in San Diego without a car. While in Los Angeles, I would mostly recommend taking Uber to the popular sites like Hollywood (parking is available though, too). Runyon Canyon park has limited parking, so going early is ideal.

Beach Hopping your way from San Diego to Los Angeles
As you make your way between the two major cities, try to stop at each beach town along the way! Here's a few stops you can make along the way. They each have a different vibe and something to offer. We swam at San Clemente, ate lunch and walked the boardwalk in Newport Beach, and got Acai bowls and watched surfers in Huntington.
Where to Eat
Southern California has some of the best food in America. Before I became pescatarian, I tried pretty much everything, including In-N-Out burgers! My sister is vegan and when we went, there were endless creative eats for her to try. We could get Acai bowls by the beach then vegan Mexican cuisine for dinner. Los Angeles will definitely be pricier for food, so I would recommend trying in-and-out burgers while you're there and eating out at more restaurants while in San Diego. Ice cream is also a must in socal, my favorite place in Los Angeles is Coolhaus and The Baked Bear in San Diego.
What to do: San Diego
I'd say about 3 days in San Diego is a good amount of time to see the main attractions.
Check out my other more detailed post for a sample itinerary.
San Diego Zoo and Safari Park
Downtown San Diego - Gaslamp Quarter
Ice Cream at Pacific Beach
Coronado Beach
La Jolla: Shopping, Brunch, Sea lions by the cove
Balboa Park
Hiking at Torrey Pines State Reserve
Old Town San Diego
What to do: Los Angeles
So you'll have about 4 days for Los Angeles, which is plenty of time to make your way around. Check out my sample itinerary for more details.
Hollywood Walk of Fame
Hiking at Runyon Canyon Park
Griffith Observatory at Night
Santa Monica Pier
Biking at Venice Beach
Drive through Sunset Boulevard
Malibu Wine Safari