Since I live in CA I thought about this one a little bit.
I agree with Dee. My list of stuff would be similar.
AR, handgun, spare ammo, water (and the ability to get more), some spare socks. and a few other odds and ends.
I would add Binoculars. I want to be able to see where and what I am headed into.
The odds and ends extra I would carry would depend on where I am headed and what terrain I am headed through as to what else I would carry and what time of year.
Leavin CA by the north you are headed into mountain and rain forests, To the north east you have mountain (Donner Pass) and to the south east is large desert. Donner pass is a different animal from May to september than from September to may. I was caught in snow and 20 degree weather three weeks ago headed back from Reno. The desert in the south is different from October to march than it is ther rest of the year. Depending on when and what way I am walking is what else I would carry. Not to mention the destination.
If I am headed to Mt ot ID I would bring a big game hunting rifle or the handgun may change.
Headed througth the desert a light weight varmint rifle. To gather food as well as engage any threats at longer range.
Swampy had a point. You can not carry the store with you, be that store, gun grocery or camping. There would not e too much more than what I carry hunting that i would bring with me. A few months before hunting season I toss everything I am going to carry into a bucket and weigh the bucket. Boots, pack, ammo, skivies, knives, everything. Weight it and fill my spare back pack with the same amount of weight, phone books and water filled 2 liter soda bottles work. I then go on daily 5 mile walks with a 9 or 12 pound Step areobic weight rod to simulate my rifle. I know it is not the 20 to 30 miles a day you need to move across a state, country or mountain but it does give me a perspective on what I can carry and gets me used to it.