Call of Duty Black Ops 3 Shadows of Evil - All Rituals and How to Unlock Pack-a-Punch Easter Egg

Completing this Easter Egg in Zombie Mode will unlock the Pack-a-Punch machine for upgrading your weapons. The good news is that you can complete it solo and by the end of round 5 or 6.
There are 5 collectible items you must find (Summoning Key, Golden Fountain Pen, Badge, Championship Belt, Hair Piece). These items are used to start the 5 rituals. For the “Beginning of the End” trophy / achievement you only need to do the first 4 rituals. The fifth and final one then unlocks the Pack-a-Punch machine. You have to do all of this in one playthrough.
You will also unlock the “From the Shadows” trophy / achievement along the way.

The video below shows all the required steps and collectible locations.