Please GOD let multiple coins to be submitted at once. I absolutely love getting rewarded for slaughtering massive mobs of... mobs, yeah, but I dread going back to my base and seeing the 3 stacks of copper coins I have accumulated. Spending ten minutes clicking in three specific spots gets real tiring in the first ten seconds. So--simple fix!
Make it so that copper, nether, and iron (maybe gold and diamond) coins can be submitted in multiples of either 5 or 10 like the mob coins for the same reward x5 or a greater reward (say submitting 10 copper coins gives 100 coins and 20 copper coins gives the same loot crate as an iron coin, so far and so forth.)
10 Copper Coins -> 100 Coins (Currency)
20 Copper Coins -> Uncommon Loot Crate/Iron Coin Reward List
I also suggest allowing iron and gold coins to be submitted for currency like the copper coins, as this would also (probably, but not that likely) fix the problem of having to spend half a decade submitting three stacks of copper coins.