Have a save right after the phone call to have the earliest possible save before any choices Have another save inside the well
After completing the game at least once, start a new game and go left for one screen and return to the beginning, to get new options for "return to camp and keep moving forward" for the last achievements. Return ending also unlocks complete the game without saving achievement.
Puzle solutions
Chest code: 94246 Tunnel code: Right Right Left Left Suitcase code: 4246 Skull chest code: 6213