When I go /out/, I either have 1 bar or zero. Often times if I'm with friends and some decide to go on a hike and others decide to stay at camp, having a means to contact a separate group of people seems really useful when phone fail.

However, will any walkie talkie style 2 way radio even be usable in the wilderness with tonnes of trees and maybe even a fairly large elevation change? Even being separated by hills?

What would be the most sensible, cost efficient and reliable means of communication with others in this scenario?