I've said it before and I'll say it again, there are four essential documents that EVERYONE should have--and the Wall Street Journal agrees. This is not only about having your wishes carried out, but also about making things easier on your loved ones when they are faced with hard decisions.

1. If You Don't Have a Will, Decisions Will Be Left Up To the Courts. And given that you don't have a personal relationship with the courts, the likelihood they'll allocate things the way you would have liked is probably slim. If you have a canned will from an online source, beware--small details can invalidate a will.
2. Durable Powers of Attorney Will Be Managing Your Money. If you become incapacitated, the person you name as your durable power of attorney is appointed to make legal decisions for you---and financial ones. Make sure you base your choice on reason and not just emotion, because your estate is at stake.
3. Medical Powers of Attorney Will Make Medical Decisions on Your Behalf. Consider somebody who will be able to stay calm and make rational decisions. Preferably someone you have had honest discussions with about your wishes.
4. Advanced Directives or Living Wills Dictate Life or Death Decisions. If something were to happen to you, would you want to be resuscitated? Kept alive through artificial breathing or feeding? This decision may differ depending on whether you are ill or perfectly healthy, but either way, it isn't fair to leave those choices in the hands of your loved ones when they are facing a tragedy. Make your decisions--and then make sure your loved ones and doctors know about them.