As a fellow PCT alum ('09) I can attest to the quality of advice presented here - if you were to follow it you would do fine.
That much said, every year is different - the weather could turn out to be very different than what we experienced. As someone who attended kickoff, it was pretty darned hot in SoCal until I reached Big Bear, then temperatures cooled down about 10 degrees and things were rather mild. Heck, I wore a rain shell walking through the corner of the Mojave. The year before it had been 110 degrees, I am told. Nothing I write here regarding conditions are set in stone.
I carried rain gear the entire time - yeah, looking back at it, in California I wore it as often in town while doing laundry as I did on the trail. But it's a nice to know that I had rain gear at the ready. Ask the Saufleys (trail angels in Aqua Dulce) about the hikers who got stuck on Mt. Baden-Powell sans raingear and without tents.
On bounce boxes - I don't know if I would send out multiple boxes by design - but people did and it worked for them. I would bounce my box (actually, a paint bucket sent priority) ahead by about 200 miles a shot but as the trip wore on, I pretty much settled on sending the box home with the instructions if I need anything, I would call. I found I used the bounce boxes more for food - sending food ahead from towns with good grocery stores to towns and in some cases, summer camps and rural post offices without a grocery store at hand.
Do send everything PRIORITY mail and do make sure to add tracking for a dollar for any gear that is valuable. You can insure boxes, I believe. You can find out more here (http://www.usps.com/prices/priority-mail-prices.htm). Boxes did get lost in the mail, it was rare, but it happened. The further north you get, the opportunities to replace gear in trail towns diminishes. The trail town get smaller and smaller for the most part.
Another consideration is there a number places (especially in Oregon and Washington) that are only served by UPS. Make a note of these - Yogi does sell a set of cards with all the trail towns and services offered - I liked the set although details do change (like store hours, PO hours, etc).
I didn't rely upon caches - this is a really controversial topic. Some advocate the elimination of caches altogether because they are a bit of a blight and because hikes have become dependent upon them. While I didn't depend on them, I miscalculated twice and was sure glad to have them there a couple of instances. Third gate water cache was particularly critical for me - it was just incredibly hot in the desert. But carrying 6+ liters is incredibly difficult (2.2 pounds per liter). I carried 4 1/2 liters and that was hard. If it is getting up to 100 degrees or so, and you are not used to that kind of weather (being from the Pacific NW, it nearly killed me), we would stop hiking around 11 a.m. or noon, hang out in the shade sometimes as late a 3 or 4 p.m., and hike into the evening. Not all the time, mind you, but sometimes the heat was just brutal.
At risk of stating the obvious, I would recommend in the dryer reaches of the trail that you don't pass by water sources without seriously considering the water situation ahead - if there is any doubt, stop, camel up. But often, i was so careful with my water I found myself carrying the same darn two liters for 20+ miles until I reached another stream. So I was perhaps conservative with my intake (well, I know I was an was often dehydrated in SoCal as a result).
Finally, one of the principles to live by in the northern climes is that the mountains can get cold, rainy, and (sometimes) snowy in fall. In summer, they will get at least cold and rainy on occasion. To illustrate, I finished October 14th. We got snowed on for several days those final couple of weeks and it was COLD (under 10 degrees at night and never much above freezing for about a week.)
The area in the north that catches a lot of people off-guard isthe Sisters Wilderness. Oregon is pretty balmy in the southern reaches generally, but by the Sisters you've gained in elevation and the area is prone to prolonged rain and wind (this is the part of the state where Oregon begins to resemble the place people imagined). Several hikers had to bail out to hitch into Bend and buy more gear because of hypothermia issues.
Food: I slept with my food everywhere but the restricted areas as well. I used a custom sized bearkidade (between the weekender and expedition). It worked great, no complaints. A hiker I met was caught and fined by rangers for not carrying a bear cannister through the Sierras - honestly, I think the weight penalty is so minor at that point (the thing weighs about the same as a liter of water and in the Sierra, water is abundant so you only need to carry a liter or two at the max.) Plus it's nice to go to bed at night not worrying about food hanging from a tree.
My best advice: Go out there, have fun, when you get beat up and tired and want to quit (which happens on occasion), take a zero day, rest up, call some loved ones, and eat what you crave. A bit of rest and time off will generally cure what ills you. The Sierras are THAT GREAT, gut out the tough parts of SoCal with that in mind!
Have a great trip! You can do it!