Birthday party at the park

We're throwing a party at the park for my son's 4th birthday. I know I want to make the Momofuku birthday cake/cupcakes. (I made it last year and I think it's the best cake I've ever had!). For food, I had been thinking of having brisket tacos, but I wonder if the brisket will be nice and hot when we get there (the park's 20 minutes from our house). We could order pizza to make it easy or I was thinking sophisticated picnic fare. Any ideas? The party will be at 4:30pm. The last time we threw him a party at the park it was easy to do breakfast burritos and donuts, but I'm not sure about dinner.