Had a shortened visit this year. Basically , Newport is the place to go for all supplies , Morrisons, Argos etc.Ryde to watch the Hovercraft and enjoy a nice seaside town. East Cowes to watch the liners . Their is a crown carvery pub between the two places at £3.50 a head ( except Sunday ) .Other than that , explore and enjoy. If you arrive early for the ferry, you can ask for the next available space !!
Went to IOW last Whitsun for a week and thoroughly enjoyed it. It's great for car touring around because no matter where you go on the island you are generally no more than 30mins away from your campsite !!
Make sure you visit the Needles Battery (National Trust if you are a member), very interesting and interactive, especially if you have children plus a nice bracing walk along the cliff path to it with fantastic views. Blackgang Chine in the south of the island is also good fun for children and adults, we are not usually 'theme park' types but this really was excellent.
Shanklin near your site is nice and there is a big new Tesco between there and Ryde for supplies.
One piece of advice I would give is to fill up with fuel before you get on the ferry, it was quite a bit more expensive than the mainland (last year anyway).