This exploit is based off of farming canned foods and painkillers. To get his exploit to work you're going to need to activate two side missions.
The first side mission you must have active is : Heavenly Gift
You will receive this side mission after clearing out Paradise Survival Camp in the beginning of the game. You will meet Chimamanda after completing her mission. She will then ask you to bring back any canned foods that you find.
The second side mission you must have active is : Kill The Pain
This mission doesn't require you to do anything but pick up painkillers
Now that you have both these missions active. Proceed through the game until you get to a point in the main mission where you meet Dr. Kessler. He will now give you some missions to complete. When you've completed the missions a fast travel to biosphere laboratory will now be available. This fast travel location is very important because when traveling to this place all the items on the map will respawn allowing you to farm any items you find. There are two locations that you'll farm for canned foods and painkillers.
The first is Mataka Village
There'll be two canned of food and one painkiller
To the right when you spawn is the first canned food, its on the the table
The second canned food is in the house on the end table and in the same house is the painkiller on back wall next to the skulls.
Now head to the fast travel and go to Marik's Marina
In this location there is one canned food and one painkiller
they're both located in the house behind you when you spawn. Just run to the right and then go in to the house. When you enter, the canned food will be on your right side on a box. The painkiller will be behind the bar to the left of you. Be careful of the zombies that are at the bar. Just run by him.
When you've picked up the two items just go back to biosphere laboratory and repeat the process over again. When you're satisfied with how many canned foods and painkillers, just go to Halai Village and return the cans to Chimamanda, then return the painkillers to Houston.