I can't answer the question in the OP. I would need to know where I am going to be, at what time of the year to answer what the most important item would be.
As the son of a Marine, I have lived in areas ranging from tidal flats to the foot hills of a mountain range. What you would need in a swamp is different from what you would need in the middle of the high desert, and what month it is would be a large variable to have to take into account. Is the area north or south of the equator? Too many questions.
basically, I would never go on the show myself. like so many other "reality" shows, it strikes me as staged BS. I have better things to do with my time, and surviving an area naked is not a realistic scenario. Surviving with just the crap in my pockets for 21 days? Much more believable.
If I have to explain why I ride, you wouldn't understand. Explaining sex to an alien would be easier than explaining the feeling, one that boils all that is going on in your life down to what really matters each time you are in The Wind. All I can say is, Life is not Life without it.