Some people have put forward some very noble ideas for what they would do with Ant Man's power and I respect them for that. I do not have noble plans for my powers. I would use them to get rich!
First I would buy one ounce of gold. Perhaps it would look like this.
Then I would make it really big and cut it into lots of pieces. Then I would sell those pieces and make a lot of money! I would only do this every once in a while; I would not want to lower the price of gold.