:: The camping trip was to an organized campground with activities for a bunch of a middle schoolers, not the "middle of nowhere." They were lost coming back.
:: They went off-road on an old road that literally no one used anymore and was not even on the maps, Ochi only knew about it because he was a local. This is discussed at length.
:: The entire valley was carved out by a meteor that left magnetic rock throughout the area, compasses are useless in the jungle too! Remember when Yuuji is trekking back up with her at the end and tries his?
:: This point is actually addressed in a la