Duplicate items:
Throw an item, including coins, into the air. Press I while the item is in mid-air, select the same item, then throw it in the air again. Repeat to duplicate the selected item.

Always have balloon:
Park the balloon outside Silmaria after it has been completed, then restart the game.

Build Agility, Strength and Vitality easily:
Hold G + K until your character's stamina is expended. Then, rest for an hour and repeat.