Yes, but you'll have to look for them.

Usually, but it depends on which islands you mean. Most popular islands (San Juans, Channel Islands, etc.) have state or national parks with picnic tables near ferry landings or visitor centers. But the really good spots—grassy knolls with a view—are rarely marked.

If you’re on a small island with limited services, bring a blanket. The picnic tables might be taken or non-existent. Check the island’s official park map before you go. And don’t rely on Google Maps. The best benches are often behind a kayak rental shack or next to a ranger