If you live in certain parts of Washington and Oregon, you'll want to be able to identify and AVOID poison oak.
Oregonhikersguide.org has a great informational page on what to look for. Consider carrying Zanfel in your aid kit and use it quickly, if you think you've gotten urushiol on your skin. It's the active agent in Poison Oak and it's no joke. The rash can last for weeks or months!
Here is the culprit. If you are not sure it's Poison Oak and it's got Three leaves - just assume it is. "Leaves of three, leave it be!"