When I was playing dying light with friend we discovered that every timw you go to sleep and wake up air drop will appear, if you don’t know air drops are pretty rare and if you collext them and deliver to one guy you will recieve lots of xp, we used that multiple times to unlock grapling hook very early. Air drops also gave lots of medicine which was hard to get in early game and that very helped us
I discovered on my own the hidden merchant chest in Skyrim, the Dawnstar one as I was looking around for either flowers or ore. I also figured out the merchants restock if you save, hit them and then reload save. Both I imagine lots of people found out but these are the only two off of the top of my head