If you haven't got enough keys of objects go to an island that has
an object you need more of. Take an object from the chest. Leave the
island and save the game. When you reload the game go back to the
island and the objects have miraculously reappeared.
To get lots of money go to the island and the guard asks you for
the silver coin Give it to him and then find the shop. Give Heimdall
all of your gold and the adamatine axe. Sell the axe and confirm
the sale then sell it again. If you sell it again you can charge as
much for it as you like.