How do you save player's backpack on exit?

I've tried using Data Store. If I do that, when I make like 50 items then it would take up to 50^50 combinations that needs saving. So is there another efficient way to do it?

By the way, I also don't want to use the old 2009 saving and loading chat script because It can occur many part of the player's inventory. Because when you use it. The player have 3 apples in their backpack and when it saves, sometimes It only saves 1 apples and when you load you can have double the amount of the apples the player had.