The procedure blocks would be "Get stack size", "Set stack size to <amount>", "Shrink stack size by <amount>" and "Grow stack size by <amount>".
The required code is:
// Get stack size int amount = ItemStack.getCount(); // Set stack size ItemStack.setCount(int amount); // Shrink stack ItemStack.shrink(int quantity); // Grow stack ItemStack.grow(int quantity);
In particular, the shrink block would be extremely useful for consumable items. Although there's a "Consume item in inventory" block, it isn't guaranteed to take the item from the active stack.