The Isle of Wight has an impressive 70 mile coastal path* that will take you a 2 to 3 days to walk depending on fitness and pace. You'll enjoy the breath taking beaches the Island has to offer as well as its famous white chalk cliffs. Overall the walking trail is rated as easy with some significant hills (you should try walking south east out of Freshwater Bay) with varied surfaces.
The route is circular allowing you to join at any point. Ryde is a popular starting point because of its train and foot passenger links to the mainland allowing walkers to arrive and circumvent the Isle of Wight without the need of a car.
Should the Isle of Wight weather take a turn for the worse the Island has a substantial bus service allowing you to continue your journey in comfort and shelter. Alternatively you can cut away from the official walking trail with the help of Ordnance Survey maps 196 or OL29.
*It should be noted that any statement of coastline circumference will fall foul of the coastline paradox.