Well, I don't know a whole lot about the XP, I have 2k and 2k3,but if they are somewhat the same, with your treasure chest:Before you add your item,make it to when your character presses it,it moves in rotation sequence like this.
<>Move Event:This Event:Turn 90*Left,Wait,Face Up,Wait,Face Left,Wait
thus giving it the opening look.then you add your item and whatever else you whant.
After this,add a switch turn on and make a page two of the treasure chest.On page 2
under event conditions, check the box and choose the event turn on switch from the previous page.Then select the sprite to the open looking chest.Then vualla,an open chest that you can only get the chest open once and only the items once!If this does not work then ask Blue Cube or Lenny.(remember this is just the rpgm2k3 way so I do not know how it will work with XP)