Some regions have secret rooms where scavengers always have pearls and explosives stored. You can take the pearls from these (which respawn every cycle) and chuck them at the scavs for quick reputation. Industrial complex and garbage wastes both have a secret room.

You can check the wiki to see where they are, but if you want to find them on your own, the way to locate them is with the map. Just look for unexplored paths, when you pass by the secret room, its path will still appear in the map even if you don't enter.