One thing that hasnt been mentioned is to use a larger antenna on the radio
Many military backpack radios from the 1960-1990s have a short-range antenna (short length, one-piece) and a longer range antenna (long length, several pieces) as part of their equipment but they can also be fitted with a much longer ranged antenna kit
This is basically a spool of wire and some cord to string it up btween trees or whatever is available. You unwind the spool to a certain length based upon the freq you're transmitting on and then hoist the whole lot up horizontal into the air and generally facing the area you wish to communicate with.
This page has an article about similar stuff. It's a long read but explains a bit (in plain language) about radio antennas and getting better range
http://www.swssec.com/ant.html