Stacey:
Don't let the Dining Plan confuse you. You may find it more helpful to look at all of your options at www.disneyworld.com under the
Vacation Packages. Choose which dining package you want (sounds like Quick Service is what you're looking for) and then look under Package Details for the arrow that will lead you to the dining specifics and the dining guide that you can download as a pdf.
My favorite quick dining places are: Cosmic Ray's for it's roasted chicken and green beans; Pecos Bill's for it's hamburger "bar"; Sunshine Season's "blue-plate" meals; Studio Catering's Greek Salad; and Flame Tree Barbecue at Animal Kingdom.
About the snacks on the plans: you get one per day on the Regular Dining Plan and two per day on the Quick-Service Plan. In general, most snacks that qualify on the plan retail under $4, but it's easiest to simply look for the snack icons placed beside the menu items in the restaurant, indicating what qualifies for a snack credit.
As for extra cash for food, that's hard to say. Typically with the Quick-Service Plan, you can use a snack credit for a
breakfast item, a quick-service meal for lunch, a snack credit in the
afternoon, and a quick-service meal for dinner. Our family usually doesn't spend a lot of extra money on food when we're on the Dining Plan because we bring a few items like apples and granola bars for breakfast and then the plan helps us stay within budget.