Welcome! I think the only way to get a guaranteed signal in the mountains, oceans, or deep canyons, are to have a satellite phone.
If they're that worried, just tell them, "Hey, if you really absolutely need me to call you, then you have to get me one of these phones, cuz that's not in my student budget
Otherwise, tell them you'll call back when you get back to civilization.
Make sure you pack a serious survival kit, food bars, lighter, matches, survival blankets, yada, yada, yada.....
Be safe and look forward to seeing ya more