i am no expert, but i do live in soCal and so most of my experience is with areas & routes where water is unreliable.
1. if this is a workable option, i would consider it. HOWEVER, here in the West trespassing can be taken very seriously and the PCT's history is riddled with public/private land conflicts. and i'd have to be extremely sure that the alternate source was reliable. it would be beyond nightmarish to hike 2 miles to an alternate source, only to find that it was dry, too.
2. yes, yes, yes. those of you who can get away with SUL packs must live in places where water is plentiful. there's no way i could do it. i am always carrying AT LEAST 2 liters (usually more) and i routinely go into a hike assuming that several of the water sources should not be relied on.
3. well, i'm one of those decadent folks who carries fresh food for the first day or two anyway. last weekend we had guacamole & chips for dinner on our first night out. it was awesome. but don't carry canned food if possible, because empty can weight adds up and some canned foods float in water that you don't necessarily want to drink/consume.
my advice is to suck it up and accept that in the desert you simply have to carry more water weight. the classic advice about not hiking during the hottest part of the day applies - you lose too much fluid to sweating & because of evaporation it's easy to not notice. if possible, hike during part of the night and sleep in the shade during the hottest part of the day. sun umbrellas can be wondeerful things, as most hats just make me overheat.