While we were at WDW last week we first shopped at Sam's Club for cereal, milk, OJ, eggs, salad mix, lunch meat, dinner meat, potato chips, bottled water, etc. Those prices were very close to what I pay here in NY. I went into sticker shock when I went to Publix and found milk to be $3.99 a gallon!! We pay about $1.99-2.19 a gallon here for milk. Produce and fruit and beer was very expensive, but most other things were close to what I would pay here. We did coupon it at the grocery store too. That really did help save about $10 on our house grocery bill. If you have a Sam's Club membership and need bulk food of any kind it might be worth taking a trip there. We ate mostly breakfast and lunch at the house with two big dinners there and then snacks for dinner on nights were weren't at the park late.
Good luck and have fun!!