SmartStack is a Minecraft addon designed to keep you in action without interruptions, automatically refilling your most-used items in these scenarios:

Block Placement: If you place the last block in your slot and have more of the same type in your inventory, SmartStack instantly refills your hand.
Food Consumption: When you eat your last food item, SmartStack refills it with more of the same type if available, so you never go hungry.
Mining: When a tool breaks, SmartStack automatically equips a new one of the same type if you have it, so you can keep mining.
Totem of Undying: When you use a totem of undying, SmartStack refills your off hand slot if you have more totems in your inventory.
Throwable Items: Whether you're throwing snowballs, eggs, or ender pearls, SmartStack refills your slot so you can keep going.
Potion Drinking: After drinking a potion, SmartStack refills the slot if you have extras.
Fishing Rods: When your fishing rod breaks, SmartStack automatically equips another one, so you're always ready to keep fishing.
Swords: When your sword breaks, if you have another sword of the same type in your inventory, it will automatically equip in your hand.
Item drops: If you drop items from your main hand and you have more in your inventory, they will be placed automatically. (This can sometimes fail)
Crossbow: If your crossbow has 1 point of durability and you have another crossbow with more durability, it will be swapped before it breaks.
Composter: If you are using items in the composter and have more items that can be compostable, it will automatically refill your hand.

This addon does not require any experimental toggle for its use.

Video Showcase:

Credits:

Credit to Minato for the code of detecting who dropped an item.

Experiments:

No experiments are needed for this addon

Smart Stack