We have always rented a car, but on our last trip, my B.I.L had to do something else outside of the park and my Sis and I and the 2 kids took the bus... it was really easy.
This year, we are going and not renting a car because we are staying on site and not visiting any other parks outside of Disney.
We contacted Garden Grocer and ordered some food to be delivered at our resort for 12.00$ delivery charge + the cost of food, they have a good variaty of food, so depending if you are on the Dining plan, you might want to get a room with a fridge and get milk and cereal, muffins, pastries for the morning etc... if so, contact them ASAP, because they book fast.
But you can always buy milk and cereal at the resort, but it's more expensive, but if that's all that you buy, it's better then to pay the 12.00$ charge.