In a few modpacks I played, I have mob farms.

In one farm, it resulted in giving me barrels full of coins. (Over 1M bronze coins)

So would like to suggest one of 2 things.

1. One or 2 blocks that auto stack or/and unstack.

Or/and

2. A toggle able command: /coins auto-stack

In which we don't need to always repeat the stack command.

Edit: Or perhaps a Bank. Infinite storage, can only store coins.