You are really asking 2 seperate questions, what can't I play without? (Jugg for me)
And "what makes this map the easiest" I believe with 3 or 4 players the easiest thing is the TANK. When it sits under the church the zombies can only climb on in 3 spots, and only 1 at a time. Not only this, but the Panzers will just stand in front of the tank patiently waiting for you to kill them. So you can sit back and headshot each zombie as it slowly climbs on, or if you get the upgraded melee, just punch your way to high rounds.
I would almost argue it's a glitch considering how easy it was to get to 35 last night with 3 randoms.