The Easter Egg is difficult.  I would recommend getting Juggernog out of the Wonder Fizz as there's only a 4 perk limit.  Also keep the Paralyzer if you get it from the box as it will be important throughout the Easter Egg.

Step 1: FILL ALL 10 SOUL BOXES
The soul boxes are Union and Confederate hats.  They only need 10 souls and will rotate a reward of either a free perk power up or a carpenter powerup. 
These are the 10 locations:
-in front of the Wonder Fizz on the right hand path from spawn
-near buyable wagon debris on the right hand path from spawn
-near CSA flag on the ground on the left hand path from spawn
-in front of the Wonder Fizz on the left hand path from spawn
-go in the corn maze from the farmhouse entrance.  Go straight until you cant anymore it'll be on the ground nearby.
-farmhouse dining room
-in farmhouse yard at the dead end corner
-in the barn in front of the portal
-at the pathway junction to the right of the barn's door
-in front of Pack a Punch (look at parts guide if you don't know how to get there)

STEP 2: INITIATE THE RITUAL
After the soul boxes are filled, rock debris will be cleared next to the first wagon on the left hand path.  It will reveal a C-shaped pathway.  Walk into it and 3 pieces will rise from the altar and quickly teleport away.  Once they teleport, go to the gramophone in front of the altar and listen to the intel.

STEP 3: CREATE ROPE FUSE
The intel will say something about raw materials that are on rooftops.  This will not be accessible through normal means.  The Paralyzer will be needed for the next few steps of the Egg.  The 1st part is on the rooftop of the barn.  The piece is cotton so look for a white piece laying on top of the roof.  Once located, fly up with the Paralyzer and collect it.  IMPORTANT: (If you don't know how to fly with the Paralyzer, look down, hold down trigger, and then jump. You wont make it high enough if you jump first.)  Also pro tip, lowering your FPS helps the Paralyzer fly higher. Once collected, place the cotton in the rope maker in spawn.  It will initiate a lockdown that will last two rounds.  Once the two rounds are up collect the rope from the rope maker.

STEP 4: CREATE CANNONBALL
The 2nd part is located on top of the rock at Pack a Punch.  It's just to the left of the PAP machine.  Once again fly up with the Paralyzer and collect the metal pipe.  Go to the farmhouse living room and place the pipe in the fireplace.  Once again it will initiate a lockdown that will last two rounds.  Once the two rounds are up, collect the cannonball from the fireplace.

STEP 5: CREATE GUNPOWDER
The last part is located on top of the house roof above the dining room.    Once again fly up with the Paralyzer and collect the ingredients.  THIS NEXT PART IS GOING TO BE THE HARDEST PART OF THE EGG.  You have to take the materials into the mixing bowl that's located in the maze.  Be warned when placed it will once again initiate a lockdown that will last two rounds.  I would recommend having Jugg Widows PHD and an explosive weapon because hell will break loose.  The zombies can run through the corn but you will not be able to, creating a hectic environment for survival.  If playing co-op I'd recommend someone stay outside the maze to ensure the survival of the game.  If you somehow make it out the other side, pick up the gunpowder from the mixing bowl.

STEP 6: PLACE INGREDIENTS
Go back to the purple altar from step 2 and place the ingredients back on their pedestals.  After they drop down, a burlap sack will spawn in front of the altar.  Pick up the materials.

STEP 7: FIRE THE CANNON
Go to the cannon in front of the farmhouse.  Go to the front of the barrel and slide the cannonball inside.  Then go to the backside and fire the cannon.  It will blow a hole in the shed revealing a gobblegum machine and the Agarthan Device lying on the ground on the left.  Pick up the Agarthan Device.

STEP 8: END THE GAME
After doing all 7 steps, the buyable ending will be unlocked in front of the barn's portal for 71,863 points.