If you wish to take in Shakespeare In The Park at Central Park's Delacorte Theater, get into the park as early in the day as possible.
My wife and I, on our daily drive through the park, have been growing concerned at the extremely long lines for free tickets. Central Park opens at 6:00 AM. The box office opens at 10:00 AM. This video was made at 8:00 AM. The line in this video (she shot, I drove) is roughly half a mile long!
So get there early. Pee first. Bring something to do, something to sit on, and perhaps an umbrella, which is good both for rain and for chilling AM breezes.