I did this walk in Boston in May 2002. We had such a great time and it was a great experience. Unfortunately, we also had unseasonable weather (hail, snow, sleet) and in the midst of fighting through, I hurt myself
But aside from that, what an incredible experience!
We (my fitness buddy and I!) trained for a few months. We mostly met up and walked on the weekends. We'd pack a lunch in our waist packs and walk one day per weekend, stopping in the middle for lunch. If I had it to do over again, I'd walk a couple of weekends both days to get the "day after day" aspect of the walk in the training.
Bring gear for all kinds of weather and wear layers. I would recommend bringing some kind of tarp or plastic piece (even a heavy duty garbage bag torn up will do) for the top and floor of your tent. Bring plastic covers for your shoes (again, even garbage bags and rubber bands will do). WE laughed at everyone that had these - until the puddles were inches thick!!!!!!!!!
Get a waist pack so that you can carry a few things and water bottles without having to hold them. There are plenty of snacks along the way for yo to grab and enjoy but you want someplace to stick the wrappers (if you eat and walk), tissues, etc. Bring two bottles for your pack (one for water and one for gatorade).
Here's another cute thing that you may decide to do: A lot of people made up shirts or hats or whatever with a picture of their loved one affected by breast cancer and wore them along the way. It was very touching to see that so many people were there for a particular person. We didn't have ayone in particular that we were walking for but a majority of people did and it was nice to see their dedications.
HAVE FUN! I'd do it again but I really should not b/c of my knee. It is just an amazing, happy event, although very emotional and touching as well.