Here are some suggestions:
Iowa summers can be unpredictable, so come prepared. Depending on which month you visit, you may need a lightweight jacket to keep warm or a water mister to stay cool! July and August are traditionally very hot so sunscreen, a hat and sunglasses are important. May and September can be cooler, so packing a sweatshirt is a good idea.
But don't worry, if you forget something you can always visit the "Island Emporium". Anything from aspirin, an extra diaper or a souvenir to take home. Lockers, strollers and electric carts are also available for rent. Lastly, don't forget, bring your sense of adventure!