Prospect Park
Let's get the low-hanging fruit of the list out of the way first. Prospect Park offers almost every imaginable picnic set-up. Want to picnic while taking in live music? Head to the grass outside the bandshell. How about a picnic breakfast while watching french bulldogs frolic in the grass? Set up your blanket on the Long Meadow. Romantic lake-side meal? Go to the Peninsula. Want to grab food from Smorgasburg? Done - it's now based in the park on Sundays.
[Photo via @l3ef]