From Dark and Darker Wiki
I did a small test: I extracted with only gold coins looted.
1st run, I looted 43 gold coins all in a single pouch, and nothing else. Result: Item Achieve and Treasure #/AP were all 0.
2nd run, I looted 26 gold coins - 2 stacks of 10, plus 1 stack of 6. Result: Item Achieve AP, Treasure #, and Treasure AP were all 0, but Item Achieve # was 3 - the same number of slots the coins took up.
3rd run, I looted 50 gold coins - I split them into 50 stacks of 1. Result: Item Achieve AP, Treasure #, and Treasure AP were all 0, but Item Achieve # was 50 - again, the same number of slots the coins took up.
4th run, I looted 62 gold coins - 49 stacks of 1 plus 13 in a single pouch. Result: Item Achieve AP, Treasure #, and Treasure AP were all 0.
Conclusion: Regardless of stack size, Looted gold coins award (probably 0, but definitely) less than 1 AP per 50 coins. So if you're looking to maximize AP gains, don't take in pouches and ignore gold coins entirely. If you care about Item Achieve # for some reason, each stack of Looted gold coins counts once per stack regardless of stack size for Item Achieve #. Gold coins stored in a pouch don't count even if you take them out later.