For the past 7 years I have done a charity ride which goes from Montreal (or Burlington VT) to Portland ME (or Boston), and covers a distance of 450 miles over 4 1/2 days - a similar pace to the ride that you are looking at. (www.charitytreks.org)

I don't know how much you ride now, but riding a lot helps. You want to have a comfortable bike, which is largely determined by fit. Many people on the charitytreks ride have sore butts. I have not had that issue, which I attribute to a very comfortable saddle (well broken in brooks B-17).

I would suggest riding more each week, and planning your schedule so that you do at least a couple of centuries before you start on this ride. Ideally, you will ride in terrain which is similar to what your ride will be like.

Food and drink that you bring with you will depend somewhat on what sort of support is offered. Many organized rides will offer you plenty of snacks and liquids.