Josh's post in this thread mentioned the wallet.
Here is my take on that same item. I use a clear, waterproof "wallet" that contains my license, credit card, medical insurance card, phone card and CASH.
When I'm out for 1 to 2 weeks on the trail my license is dual use, ID and the ability to drive to and from the trail head. The credit card and cash are for the trail towns and resupply points. The phone card is for the ability to stay in touch in areas without cell phone service when I have to resort to using pay phones in trail towns.