Flip flops are a must
Sailing across the water on one of the ferries to Shelter Island is almost immediately reinvigorating. If you drive you absolutely must get out of your car during the ferry ride. Shelter Island is both a casual vacation spot as well as a laid back place to live, a place to eat right after leaving the beach still covered with sand. It is a family friendly/pet friendly environment. And don't forget your flip flops during the summer time.
This can be seen best by an experience I had at the Vine Street Cafe located off of 114, aka South Ferry Road. This restaurant is awesome. Great food prepared and presented with care using all local and seasonal product, attentive service, and a well diversified wine list. I was sitting out front of the restaurant and watched a couple ride up on their bicycles. And yes, they were there for dinner. I also saw one guest bring their very well behaved dog to dinner. They of course sat outside with their sweet pooch tucked under their table while they enjoyed their dinner and wine.
There are also many other things to do in and around Shelter Island. On the island there is a fantastic state preserve which is quite beautiful to explore both by car and on foot. Mashomak State Preserve is the name. And of course there is the beach, which if you're lucky you can claim one of the fun beach chairs that are provided. Rent a bicycle or kayak to explore both by land or sea. Look for Sunset Beach Hotel and Restaurant across the street to grab an early glass of wine before it packs out for the evening.
On the North Fork of Long Island, a quick ferry ride away, there are many many different local wineries with tasting rooms that are open just about every day. You'll also see fresh vegetable farm stand after farm stand driving down the main road through the North Fork. If you go to the South Fork by way of the South Ferry, you'll find Sag Harbor with a lot of fun shops and good food. Just look around. You'll see what I'm talking about.