What's up all? First post here.
Couple of things. I hiked the roughly the last 25 miles of the JMT (we came in at Bubbs Creek) to the top of Mt. Whitney in the beginning of August 3 years ago.
First, especially the latter part of the JMT that I did, it gets cold up there in altitude at night (you're above 10,000ft the whole time). One night was as cold as 26 degrees, albeit we did camp just passed Forrester Pass, a little below 13,000. You will definitely want your sleeping system (whether you choose a bag or quilt) rated to 20-25 degrees.
As for the Dr. Bronners. That is a rough one as toothpaste, but suffices. I'm weird about brushing my teeth and toothpaste is a small weight sacrifice I make. One thing to think about with DR. B is how scented it is, especially the standard (peppermint). You wash yourself with it and that's all you smell. While stinking of green bubble gum isn't the worst of things, bears might find it interesting as well. I've been using "No Rince Body Wash" for a bit now, and I love it (http://www.rei.com/product/824348/no-rinse-body-wash-8-oz). It's unscented, so perfect for bear country, and easy as hell. Just rub on skin, and wipe off with a dry towel (or bandana).
Instead of Gatorade bottles, try Smartwater bottles, taller and thinner, they pack quite nice.
Definitely want a beanie. Northface makes a nice merinol wool one that has a fleece wrap around the bottom half of the inside for double warmth on the forehead and ears, while leaving a little more breathability on the top of the head.
As others have said, ditch the rain pants. I got rained on twice and snowed on once while hiking on that trip, I was just fine in the nylons with thermals underneath, never even noticed it. In the case of the little bit of snow we got, we just set up the tarp and chilled under there. Good nylons will work just fine.
As for trekking poles. When I did this hike a few years ago, my friend and I were both sans poles. Of all the people I met on the 84 mile trip (42 miles each way), and there were a good amount of people we met, mostly seasoned backpackers, I think there was 1 other person besides us not using poles… Really had me thinking. Now I own a pair and I won't backpack without them. Just my 2 cents anyway.
On a final note, I do hope you plan on summitting Whitney at the end of your journey, it's an amazing view and totally worth it. I'll actually being going again in the middle of August with a couple of buddies (13th to the 19th, 7 days, 72 miles coming from the south up Cottonwood Pass and atop Whitney, then back). We're doing the summit the same as we did last time, hiking up at night and watching the sunrise. Stunning…