Life have been harsh early on, born outside the system and growing up in a trailer park far out from the rest of the human population gave a bit of basic skills to survive on your own when you have almost nothing and have to go by on what the nature gives.
Hiking, living in the nature as much as possible was a way for him to escape the everyday life where people were sniffing glue or gasoline to get some kind of joy from the bitter and ugly life they lived.
Jack managed to stay away from that kind of lifestyle more or less.
His parents died when he was almost "grown up", even if age did not matter where they lived, drinking themselves to death on some homemade brew that not even the rats would taste, so family and friends are something thats not too natural or familiar.
With almost nothing to his name and no proper education Jack decided that he will hike around the world, helping out farmers, locals and so on with whatever he can to get the basics, food/water, shelter and maybe some clothing, his most recently trip took him through Georgias lovely trails, going close to the green sea, touching Russia a bit before ending up in Chernarus.
By walking the more famous trails when everything went down he managed to stay away from the chaos and fire, he knew something bad was going on, there was no way to avoid it, even if you wanted to, considering he was in the middle of the cooking pot.
He did not know how bad it was until the trails he walked became more traveled, first, by fleeing animals at the early stage, then humans came, filled with fear.
After the humans, they came.
When the world went to hell he felt kind of happy in one way, now everyone would live as he did.. in some way, if you disregard all the death and fear that came with it.
Makeshift beds and homes, scavaging for whatever food you can get, looking forward to the next hot shower and so on.
He decided to put his skills to good use, so he stoped hiking and started hunting, seeing food was much needed, specially cooked.
Jacks plan was to make sure everyone he met always fell asleep or parted with a full belly, never hungry.