Snakes sold at PetSmart are carnivores and should be fed an appropriate-sized rodent. PetSmart recommends that you feed your snake frozen mice (called "Arctic Mice" in PetSmart stores) or rats, which are considered safer for your snake. Feeding frozen, thawed prey reduces the chances of disease and parasites in snakes and reduces chances for injury. Most juvenile snakes will start out on "pinkie mice," the smallest variety of frozen mice. You should increase the size of the mice as your snake grows. As a general rule, the diameter of the snake should be consistent with the diameter of the prey.
Juvenile snakes should be fed twice a week where as adults are fed once a week. If your snake doesn't eat within four hours, remove the food from the habitat. Snakes may not eat immediately prior to and during shedding. Give your snake some alone time to digest after feeding. If a snake is handled too soon after eating, it may regurgitate the meal or become more difficult to feed.
Your snake will need a water dish for drinking and soaking in. Use a heavy dish that's shallow and tip proof.
If you find your snake lying in the dish, he may be preparing to shed and you should double check that the humidity in the habitat is at the appropriate levels.