Where do I start? Great question! With so much knowledge and so many skills related to backcountry travel and self reliance, how do you prioritize them? If one must, here is our take:
Land Navigation - the vast majority of civilian survival incidents start with getting lost. Therefore, your number one survival skill and a key to backcountry enjoyment is effective land navigation. Here's a quick video primer, but you'll need to practice these skills on the ground. Craig Caudill literally wrote a book on it. RAT also teaches courses that cover it.
Stop the Bleed - this is one of those low likelihood / high impact skills that is quick and easy enough to learn that you should get to it sooner than later. Dark Angel, SOS, and Ugly Puppy all teach it.