Here’s another idea: nukes.
It would be an upgrade for your missiles,which you can get for 100 keys.(might need to be changed since I still don’t know how hard/easy it’s going to be to get keys in ciu). Just like the scoring unlockables,it will only have effect in new games. The food requirement for obtaining a nuke would be 75 food items. It will travel the same way a regular missile would. Once it explodes,it will destroy all enemies that are both on-screen and off-screen in the current wave. Also,it will ignore the splash damage resistance some of the enemies have(like barriers,which can only take up to 500 damage from missiles). However,it will also reduce your power level slightly.