Infinite Gold: 
Start a new two-player game and load up a character with gold in their possession. Get them to drop their gold and pick it up with the 2nd player's character. Save the 2nd players character and then quit the game without saving player 1's character. Repeat as necessary.

About the Infinite Money:
You cant put the money on the ground or they will start to disappear. I use that cheat but you just got to keep the money in your inventory.

Duplicate belt Items:
To get infinite items you have to drop 9 items in a square and stand in the middle and act as if u were going to drop an item by pressing X on a belt item and then press.. Triangle.. and you will have 2 of the belt item.

Premium Items:
To get new premium items save the game in front of Grizwald. Then reload the game to get a new list of premium items.