I agree 100% with the PP's who said that October is unpredictable in SoCal. And early October can be a 180-degree difference from LATE October! I also agree that I wish it were COLD! I am sick of heat here in L.A. I want a nice cold snap! October can range anywhere from high temperatures close to 100 degrees (and I will die if that is what it turns out to be when I go in a few weeks) to a nice mild 70 degrees! It is usually dry, very dry, so keep that in mind if you have allergies, sinus problems or asthma. Drink a lot of water. The dry and often windy weather of October is what fuels the terrible wildfires all over SoCal. If it is even remotely windy, DL won't do the fireworks at night. But, then, sometimes in the latter part of October, it could be pouring rain. I would say that you will be safe wearing Capris and a t-shirt or tank top in the daytime - maybe even shorts - and then a light jacket at night, if you get cold easily.
For me, it is not cold until December/early January, where sometimes, if we are lucky, it might drop down to 30 degrees at night! I LOVE that time of year!