simply go around most camp sites during the campaing particularly during the Adapt phase of the campaing. After a main mission, strole around the packs of soldiers that are speeking together and you might fall on one mentionning a lonely armor or a wreakage to loot or a companion who, having been shot but a sniper, needs avenging.
Once the task has been assigned (right after you hear the soldiers speaking about the matter), you may look at your map and find a new marked zone to get to so to take care of said mater.
There is very limited info in most cases so you are alone, in the dark (not always literally) since this is merely a patrol with no info backing you up. You ight cross a patrol, you might find too much for you to handle...
This, I find, is a great add on and helps breaking the story that would otherwise be carved in stone timewise. (mission 1, then 2, then 3, then 4, ...)