We always bring milk, water, soft drinks, etc with us. We also bring cereal, doughnuts, cream cheese and crackers, lunch meat, bread, cheese, plenty of chips and pretzels, (buy the small packs that you would usually pack in school lunches-you will have more of a variety) you can even buy dip. I go down to the food court and grab some condiments for our sandwiches. I even bought some tuna packets (from Sams) there are crackers, low fat mayo, relish and a spoon already inside for you. (Great quick snack). We do splurge and go to a few resturants inside the parks. My husband and daughter always have to get popcorn in the parks-they swear its the best popcorn.
We always head over to Walmart for some inexpensive souvenirs. They have the same things that are offered in the parks except they are way cheaper. Of course they do not have everything, we do usually splurge on 1 or 2 souvenirs in the park.
If you have little ones, you can always pack a few snacks in your bag for the parks. Bring a few baggies and put trail mix, pretzels, chips, etc for a quick snack through out the day. We are big water drinkers so we always have our water bottles. We were there this past July and Disney now allows in small soft sided coolers. My father is a diabetic and carried around a small cooler with ice and water, etc inside. I think it held about 4-5 water bottles.
Have fun!!