If you're in for hiking, Mt. Doug has some great views and good old caches.
is a good cache, Ten Mile Point is a nice area.
Island View Beach is another fine place to visit, here's a cache in the area: GC113P1
Also, on your way up island through Nanaimo, GC139EH
offers a good place to stretch your legs, as well as a fun cache to find.
Hope you have a good time visiting the island!