You live near my neck of the woods, are you driving?
If you are driving you can bring an ice chest with you with milk, soda, juice, yogurt. Then bring other things like cereal, bread, bagels... I see you have a 2 yo. You could bring fixins for a PB&J and give that to her in the park for lunch, bring a little cup of applesauce and you've just saved yourself $6 per meal