Use sites like Steep and Cheap, I suggest knowing what you want and watching for deals if you have the time. Also, this is a great gear reference: 10 lb Backpack.
The other stuff:
Navigation
I read the book to help prep. I made little notes in it and used it as a reference point and to help me feel less insane since everyone I knew thought I was crazy for deciding to walk across the country. At least this Yogi person and the people that answered the questionnaire understood my mania.
The book comes with “beta” pages or tear-out pages about sections of the trail. They included phone numbers, diagrams, notes from other hikers. Jonathan and I shared a copy. I saw these pages only a couple of times, but the info was quite useful.
I love this app. It’s free. It’s accurate. It was reliable. I wish Halfmile made an app for my everyday life. “You are 2.2 miles off trail for your life. Get it together. The shortest distance to achieving your goals is ...” I could use support like that. I miss looking at this and knowing where I was, where I needed to go and the fastest way to get there.
If you are hiking with a smart device, this is the way to go.
While using Guthook and Halfmile I could answer most questions about the trail. Guthook costs money, each section was $6. You can buy the whole suite of apps for $30, I think. Go for it, although if you are on super strict budget, you could get by without.
Water storage
Smart Water bottles and a wide mouthed Gatorade bottle. Don’t carry Nalgenes for they are heavy.
Maybe use a platypus or camelbak container for the ease of packing. In the desert I carried up to a 6 liter capacity using plastic bottles from gas stations. They're light, durable and cheap!
Water purification
AquaMira - Mix part A with part B. Wait. Add to bottles. Wait. Drink. Tedious but effective as long as you use it correctly. Chlorine Dioxide (active Aquamira) /= bleach.
Sawyer / Squeeze (3oz) - This is a great purification solution. Compared to the pumps and thing I used growing up, you can't ask for a better innovation. That said, using it every day gets old fast. Its not as quick as using drops because you have to fill the bag and squeeze it, which can get more difficult with dirtier water. Also, the bags can break or leak and contaminate your clean water. The filters do fit on several water bottles, which helps with the bag issue. For me - this is for short trips or back up/emergency water purification method.
Bleach (household bleach is typically Sodium Hypochlorite, although you should always check the container for potency and composition if you are planning on using a chemical to treat your drinking water)
Treating water with bleach is definitely effective, but there are certain risks and may not be able to destroy cryptosporidium pathogen with 2 drops in a liter. I used bleach to treat water from Northern California to the border and have used bleach in the past very frequently. There are plenty of studies out there discussing the use of bleach as water treatment. I would consider reading up on water treatment. Start with the CDC or something.
Misc
I carried a myriad of other items in my backpack. These included a harmonica, an iPhone, iPhone charger, sketchbook, pen and pencil, permanent marker, some paper, my hiking permit, and some money and credit cards. These extra things can add up fast. Your friends may put rocks in your pack. You might put a beer in your bag to have on the first night then forget about it (great surprise when you do end up finding it later, though). It's a fun trip, enjoy it. Try not to flip out about gear too much. I'm sure while you are planning your trip you will freak out a few times... once you are on the trail, stop doing that.
Cheers,
Dan (aka Soapbox)