A RABBIT NEEDS FOOD, HAY AND WATER TO STAY HEALTHY - I'm not going to go in depth here about the importance of food, hay and water. This post would be much too long! I've posted about all these three before under Hay, Pellets, and Water.
A RABBIT DOESN'T NEED TREATS TO BE HAPPY, BUT SOMETHING A LITTLE EXTRA NEVER HURT ANYBUNNY: See more about this here.
RABBITS NEED PROTECTION FROM THE ELEMENTS, HEAT AND COLD - This one is self-explanatory pretty much. If you have a house rabbit, this is easy. If you don't, keep it in a traditional wooden rabbit hutch instead of one that is all-wire. Rabbits are very exposed in these all-wire cages, so usually if a breeder is going to use them they are either kept in the house or in a shed. Because of their fur coats, rabbits do not need anything to stay warm, and they do better in cold weather then in hot.
RABBITS NEED LOVE, ATTENTION, AND HUMAN INTERACTION AS OUR PETS - In the wild, rabbits live in communities in their underground warrens, living together, playing together, and grooming each other (this is why domesticated rabbits enjoy petting. It is what they are used to receiving when they live in groups).
Rabbits would get VERY lonely and sad without a friend. If you don't have much time to devout to a rabbit, consider getting it a bunny friend. Read more about that here.