My wife and I hiked N. Manitou last summer. It's a great back-country lite hike right in our backyard. Beautiful views and some interesting history. Many old, overgrown orchards to hike through, old shipping dock remnants, old barns and other buildings to check out. We packed our stuff around everyday, but the island is small enough that you can set-up a permanent camp and then day-hike around. There's easy access to water nearly everywhere so it's possible to carry a minimum of water and a filter to refill bottles. The north side of the island is the most underdeveloped and wooded. It also has some pretty significant relief near the water's edge, so not super ideal for camping and it can be pretty buggy. Has great views of the Fox Islands though which are pretty hard to see from land unless you're in the right spots. Easy boat ride from Leland.
Can't wait to do it again!