Nowhere but there would be a very useful gobble gum.

Spawn a Bonfire Sale Powerup could be one

spawn the mini boss for the map at anytime??

Name: Lizard Stare
Affect: For (x) duration, the player emits a deadly beam from their face killing all zombies it touches.
Text: It's rude to stare.

I typed this up in the comments and then saw there was this thread. What about a Green Gobblegum in which taking damage gives you 100 points and lasts 60 seconds? (Inspired by Call of Duty: Infinite Warfare's Punching Bag$ Fate and Fortune Card.)

Name: The Summer Sale
Effect: Acts like Reign Drops but spawns 9x Firesale Power-ups
Could be reduced to however many to make it balanced

name: wonder box
effect: give the player a random wonder weapon from the box

name: begone boss
effect: kills all bosses for that round

name: perkaholic on me
effect: gives a random player a perkaholic

name: test your luck
effect: spawns a bonus points that has a chance to give you points or take your points away from you

name: no one left behind
effect: when active all players will be teleported to that player

name: no ammo no glory
effect: when your gun reach 0 it will use 2000 points to refill all your ammo

name: who cut the cheese
effect: turns all zombies into cheese and your knife is a instant kill

name: all hell broke lose
effect: all zombies are on fire

name: sharing is caring
effect: when active a weapon from the box will become a drop and any players can get it