The amount of $$$ that you'll need for food will depend on your dining habits and expectations. If you plan to do character breakfasts and sitdown dinners, the costs can really mount. If you plan to bring breakfast foods with you, counterservice dinners and sharing meals, you'll need much less.
For your family, the MYW dining options would cost $90 per day ($35/adult and $10/child per day). With it, you would get one sitdown meal, one counterservice meal and one snack each day. This would bring the food budget for a 6-night/7-day stay to $540. To me, this sounds like a good deal as long as it doesn't mean that your room rate will increase dramatically as a result of changing from a room-only ressie to a package.
Now, if your kids are not big eaters or less tolerant of sitting through a meal that includes appetizers and dessert, you might want to be more flexible with your dining plans. Check the menus at
AllEarsNet.com to see what is offered at the various WDW dining establishments and what the meals cost. Don't forget that the tax in the food will be 6.5% and that you should add a gratuity for your server at sitdown restaurants. Sharing meals is allowed at most venues, with the exception of dinner shows like Hoop-de-doo and buffets.
My own personal experience has been that my family of 4 (DH, DD14, DS12 and myself) spend about $125 per day on food. We usually grab a quick breakfast, do a sitdown lunch and then do counterservice dinners. I use the meal vouchers to help bring down the costs. We share 2 adult vouchers at lunch and suppliment the meal with additional entrées and beverages. We never go hungry.
With regards to the SeaWorld tickets, the best price is the 20% discount that SouthWest Airline Rapid Rewards members get at the gate. You can join Rapid Rewards at
Southwest.com - Rapid Rewards . Just show your card at the gate for your discount.