This mod edits not only the drop rates of the loot bags, but also the tier. The 3 tiers are the yellow, blue, and orange bags, with orange being the best loot. (Regular, Strong, Boss is what they're referred to in the game files). Adding specific items into the respective loot pools is also in consideration (i.e. gyrocopter parts being in the Boss loot bag pool).
MAIN:
Adjusts the loot bag drop rate for ALL zombies. The exception is the Demolisher, who is default 30%. There is a separate module to increase his drops.
Alpha - Increases drop rate from 2% to 10%.
Beta - Increases drop rate from 2% to 15%.
Charlie - Increases drop rate from 2% to 20%.
Delta - Increases drop rate from 2% to 30%.
Echo - Increases drop rate from 2% to 50%.
Foxtrot - Increases drop rate from 2% to 100%.

BONUS:
Alpha - Makes ALL zombies drop blue loot bags, or better.
Beta - Makes ALL zombies drop orange loot bags.
Charlie - Increases Demolisher drop rate from 30% to 50%.
Delta - Increases Demolisher drop rate from 30% to 75%.
Echo - Increases Demolisher drop from 30% to 100%.
Foxtrot - DECREASES the loot bag despawn time to 2 minutes. Default time is 20 minutes.
Golf - DECREASES the loot bag despawn time to 5 minutes.
Hotel - DECREASES the loot bag despawn time to 10 minutes
India - INCREASES the loot bag despawn time to 30 minutes.
Juliett - INCREASES the loot bag despawn time to 50 minutes.

ADDON:
Alpha - This will INCREASE the despawn time of backpacks spawned from closing a temporary container (i.e an ammo pile) to 10 minutes. Default is one minute.
Beta - This will INCREASE the time it takes for your characters backpack to despawn after death to 2 hours. Default is 1 hour.