There are a few things that you should make a point of leaving at home.

• Copies of your documents – Minimally a Xerox or digital photo of your passport, drivers license, credit cards, airline tickets, and any reservations that you’ve prepaid. Having someone fax or e-mail these things to you in a emergency could literally save days of hassles if you need to replace them.
• Cell phone. It probably won’t work and if it does it may be quite expensive.  Read up on cell phone options for Costa Rica before automatically slipping yours in your pocket.
• There is no point in carrying all of your keys. In fact if you take a cab or airport shuttle the only key you need is the one for your home. Leave the rest in a safe place. Since you won’t need your front door key while you travel, it’s a good idea to safety pin it inside one of your bags or suitcases rather than carry it around in your pocket. Make sure the remote for your car door locks/remote ignition isn’t in your pocket when you go rafting!
• Wallet contents- If you’re going to carry your wallet, you can probably remove ¾ ths of the contents. You won’t need your library card, health-club membership, or the receipt and warranty card for your new lawnmower etc.
• Purse- This is a controversial call. We’ve seen purses that contain everything from an emergency operating room to the better part of an automobile repair shop. Look at what’s in yours to decide if you want to lug it around, and if there is anything you don’t need to risk losing (see wallet above).
• If you’re visiting from the U.S. or Canada you can leave the electric converters and plug adapters at home.  The current and plugs are the same and your appliances should work just fine.
• Sheets/Sleep sack-great for hostels in Europe, but not necessary in Central America.