Show up at the Southold Yacht Club on the morning of the race (7/12). The sunfish start first-around 10am. The cats start 10:30-11am. Most sailors set up their boat in the parking lot and roll them onto the beach. We've had as many as 12 boats. It seems like there may be more interest this year. This website has a marine store that stocks all kinds of parts and supplies for cats.
It's something like $30/person. You get T-shirts, food and trophys. It's a good deal. I can't speak for them allowing boats that aren't Sunfish in the Sunfish class. They get enough sunfish anyway. We need more cats.