Related: a few years ago, I researched advance medical directives. They're surprisingly easy to make in the USA. They made a federal law about it in 1990, so you just have to fill out a short form (which differs for each state). The forms for each state are all available here.

The main decisions are:

• designating someone to make health decisions for you, when you're unable
• providing general guidance on whether to prolong your life in various situations
• whether it's ok to donate your organs to others

Fill out the form, store it and some copies somewhere sensible, and you're done.