Even though breastfeeding is natural, it doesn't always come naturally. If you are planning to breastfeed your baby I'd recommend learning how to do it before you have to do it. There are classes out there but you could probably do just as well reading a book. These are the things I found necessary for successful breastfeeding.
The Nursing Mother's Companion. This is the best book out there and you'll be glad you have it. I went back to it time and time again with my first two babies. It was invaluable.
The phone number of a lactation consultant. Many women have difficulty in the beginning and calling a lactation consultant within the first couple days of breastfeeding if you are having pain or problems with the baby latching is one of the wisest moves you can make. Ask your doctor for a recommendation ahead of time.
My Breast Friend. I had a Boppy with my first baby and I think it actually caused some of the problems I had breastfeeding. I got a My Breast Friend and love it 100 times more than a Boppy. Of course, a boppy comes in really handy when baby is learning to sit and a MBF isn't useful in that way, but I digress.
Lily Padz. These are the best there is when it comes to breast pads. At first you'll definitely want something that absorbs more so get some disposable pads. The cloth ones don't hold much.
Soothies. I loved these for the first few weeks. I am the only person in the world that had an allergic reaction to Lanolin (which is highly recommended as a way of soothing sore nipples).
Nursing Tank. I wore these almost exclusively during the first month. The soft cotton was way more comfortable and it was easier to get a little air, if you get my drift. I prefer the kind that you unhook the clasp and lower rather than the kind you pull up or down. I can't find a link to my favorite kind but I got them at Motherhood. You'll need nursing bras too but I can't make a recommendation. I've tried a lot of different ones and with each baby found I preferred something different.
Breast Pump. Which one you get depends on what you need it for but every nursing mother will need one if she wants to ever feed baby a bottle. I had a hand pump with my first baby and hated it and therefore didn't use it. It took a long time and was difficult to use. I got an Ameda Purely Yours with my second and I am so glad I did. A double pump electric is way more efficient. They are a lot more expensive than hand pumps so it is up to you what way you want to go. If you plan to give daily bottles or work you really need an electric double pump.
Bottles. Don't go nuts buying bottles before baby comes along. Unfortunately, babies are often picky about which bottles they will drink from so you might have to experiment with different types. My girls actually tended to like the cheaper Gerber bottles the best.
A nursing cover is nice to have but not absolutely necessary. I started using one with my third baby and it is nice when you are in a restaurant or at your in-laws.
Here is my best breastfeeding advice for the first few weeks. Always get comfortable and get a glass of water first. Sit somewhere your feet are firmly on the ground (or a stool). Don't slouch over, put a pillow behind you if need be. If baby isn't latching correctly, don't be afraid to start over again and again until you get a good latch. If you are having pain, call your LC. Air out as often as possible to help with any healing that needs to occur.
What did I miss? Did you find all of this necessary or is your list of "must haves" shorter? Any good advice for the newbies?