Walk down into town and head for the ferry steps (from the town beach at low tide).  Take the ferry over to Rock and turn left along the beach or on the Coast path (accessed through the car park).  At low tide you can walk all the way to Daymer Bay on the beach.

 

Walk round to Polzeath for coffee - try TJ's Cafe (on the beach above the surf shop).  Then head back to Rock for lunch (The Blue Tomato Cafe is near to the ferry point and has a nice open air eating area if the weather's good).