i would say since its at the park it might be a cute place to have someone grill up some hamburgers or hotdogs, maybe both. perhaps a side of salad, then maybe one of those platters that has celery, carrots, tomatoes etc with ranch would be cute to let ppl snack on the rest of the time before and after the real meal.
Idk if people are going to be there for 4 hrs I would expect a little bit more then just finger foods! I'm having mine from 2-5 & were having a meal chicken,Italian beef sandwiches couple sides like potatoes & salad & cake!