Porkyupons is an item dropped by enemies but was edited out of the game before release. Information about this can be seen in the secret Memo Menu. They are tradable for money at "Redemption Centers" with each having different rates for coupons.
It seems to be a beta version of making money in Mother 3 instead of enemies just dropping them. I wonder how fun it would be...
 Memo Description
- Let's say an enemy drops a coupon when it's defeated in battle.
- In your case, what would you do with it?
- Use it as a bookmark or something? That maybe a wonderful way to make use of it.
- But take it to a Redemption Center, they will actually cash it in for m-m-money!
- Each shop has a different rate, so be sure about it before you trade.
- You can redeem up to 100,000 Porkyupons at a time.