A cell phone (smartphone) can be much more useful than just making/receiving phone calls (even when not in range of a cell tower).


Here are things it can do even when not in range of a cell tower:

Most now have a GPS.
Many also have a compass app.
Many can store off line topo maps that will work with the GPS.
Together these can track your trail on the map.
They can measure inclines and distances.
They can store medical reference manuals, or edible wild plants info and pictures, etc., etc.
You can make electronic notes.

I put mine in the top 10 (including either a spare battery or a solar charger).