He doesn't need water or formula or cereal, and giving supplements of any kind may interfere with his appetite for nursing and lead to supply problems. It's best to wait until breastfeeding is well established before introducing artificial nipples of any kind. No matter how much you eat, your baby will get high quality milk, but if you don't eat enough to account for the extra calories, you may start to feel tired and run down. Getting dehydrated can not only make you feel lousy, but can affect your milk supply. Get as much rest as possible, sleep when your baby sleeps, lay down to nurse as often as you can, and have someone else tend to the house for a while.
Fatigue can aggravate breast infections.
If you have any problems or concerns at all, enlist the help of a fellow breastfeeding mother or get help from a LLL Leader or Lactation Consultant. These are some tips I have either used myself, or have had people tell me work great. If you get engorged when your milk first comes in, alternate ice packs between feedings, with warm compresses just before feedings. To make a handy hot compress, take a small disposable diaper and pour about a half cup of water into it then microwave it for about a minute. The diaper will stay hot for a long time and doesn't get you wet the way a hot washcloth would.