Lockpick is a very useful tool that allows you to open many locked caches with valuable items inside. You can obtain it very quickly after you reach the Soviet Installation. During the main campaign, you meet a person that may task you with "Cut Short". It is available in the Logging Camp - talk to the man there. Thanks to this, five radio towers will be added to your map.
You can see targets of the mission from afar and you can tell them by the lights blinking in the distance. They have been located within a short distance of each other, which is why locating them is not too much of a problem. You are going to indulge in some climbing and, depending on your progress into the main storyline, some combat, if you want to get to each one of the towers.
As soon as you approach the repeater, you only need to destroy it with your hatchet. As soon as you do the same with the rest of the towers, return to the man to receive the lockpick. You can now open all of the locked Chests and doors.