Well damn you thought five nights at Freddy's was over and personally I thought it was over as well but . Someone had said that it unlocks something called " .. 5) mentioned that in the The End screen there is a "?.
There was also a rumor stating that entering 5 into the Custom Night settings will unlock an easter egg for Five Nights at Freddy's 2. This has been proven.
Cheat/Hack for FNAF Sister Location to unlock all nights, extra menu, and exotic butters. Go to your start. Documents from Phone Guy revealing similar information as Purple Guy's notes theoretically would. Go to your office on any night. We've got you covered. Could Death Stranding Ruin Kojima? But even I accept that Five Nights at Freddy's is. Maybe what's in the chest is everything about FNaF.