Do you have time there to grill something simply like burgers or dogs, is that allowed there? Is there a place to plug a crockpot in at the park?
What about packing a to go breakfast? We do this if we need to be out of the house early for some reason & have no time for breakfast. Basically it can be anything, we usually do a peeled hard boiled egg (easy to peel at home), a muffin, a baggie of dry cereal, an apple or grapes or an orange (can peel the orange at home), yogurt or go gurt, and then something to drink, a thermos of water, milk, fruit juice, whatever. I’ve always premade breakfast burritos and put in the fridge or freezer to microwave right before we leave before.
What time are you eating supper? Sometimes grocery stores will mark down their roasted chickens after 7… you could eat it as is or slice/ shredded right in the little pan they come in.
If you pack breakfast and lunch to take with you, make something Friday maybe then you just have to grab and go… even if you end up getting supper out or at the grocery store deli or whatever, its still cheaper than eating all 3 meals out or from the grocery store.