High tops, denim, stripes and a relaxed linen shirt are perfect for the park in 'the Fall'. Tan is a nice contrast against the muted blues palette. If it gets cooler try a heavier cotton layer in place of the linen, white sneakers would be ace also. Jac & Jack ensemble, Persol sunglasses with Aquila high tops.
Tip: Have a picnic without your phone, your brain will thank you.