First off a word of warning, the area around the Cache Location is very swampy, even in June when I placed it, so I suggest some appropriate footwear
Finding the Ammo can other than the terrain is easy, getting into the Cache container is another story.
I will not say much more other than you do not need anything other than what is there at GZ to do the Field Puzzle.
Depending on the time of year I also suggest you wear insect repellent as it was nasty there when I placed it.