check out some of the past messages in regards to foot care, bodyglide etc, and there is lots of info already posted that will help answser so many of your questions.
You don't need to take a lot with you as you're really taken care of on the walk. No need to carry any weight around. You do need to bring your own water bottle, there will be lots of opportunity to fill it up with water and gatoraide at the pit stop and water stations. I've always worn a fanny pack that held my bottle, and in the fanny pack, I put my ID, some cash, credit card, extra socks, (good idea to switch at lunchtime) some people carry some moleskin ( in case of blister hotspots), bandaids, a small thing of body glide, and necessary medication. At the Med tents, there are lots of bandaids, advil/tylenol, sunscreen, vaseline. There is tons of food. Oh, I take my cell phone to.
so really, you don't need a lot, Over the past 6 years, I've seen people with these huge packs, and always wondered what they needed that for.
Hope that helps! I'm sure there will be lots of other suggestions to...
What to wear depends on the weather, of course, but whatever you decide to wear, make sure you have washed it and worn it on a long training walk to ensure it does not bind or rub or chafe you anywhere. That way you know you will be comfortable and that is very important when doing this walk. Keep watching the message boards for more tips, and most of all... Have Fun! You are doing something great!