You can pick up a waterproof wallet at K-mart, Walmart or Magellans.com.
It will fit around your neck or around your waist and tuck into into your trunks or fit into a zippered pocket of your bathing suit. They work great. You can also go inexpensive and use a zip-loc bag for your credit card, ship card and cash. Leave the rest of the stuff on the boat or shore.
These things still work just fine if they happen to get wet.