You might consider La Jolla Canyon, north of Malibu and Point Mugu, near Leo Carillo Sate Park. There is a backpack-in camping area on the plateau above the canyon. You have to hike several miles and probably a thousand vertical feet of climbing but it is a pretty trail. There's a waterfall along the way and a pond near the plateau.
Once you are at the hike-in camp, you can set a base camp and day hike around the area. For variety, there is an exit trail that goes out to Pacific Coast Hwy via Sycamore Cyn to the south and another (very steep but safe) exit trail to the north.
The nice thing about this area is that it stays cool in the summer, unlike that 100+ degree Angeles Forest overnighter that we did a couple summers ago.
I imagine there are campfire restrictions but I expect that's true in a lot of SoCal.
Anyway, that's one option to consider.
DancesWithKnives