Finding Items from vase, crate, etc.

I have set an event for my player to find an item from a vase. It is triggered by action button. I need to know how to make it so you can only gain that item once, even if you change maps and come back. I would also like to know if there is an easier way to do that instead of making a whole other map w/o that event. Please tell me if these questions are unclear so I can elucidate them.

use a self switch

create an event and make the grafic out of the maptileset of the case
then choose the event to gain an item, after that make it turn on self switch 1
then make a new event page with the same grafic and have it turn on when self switch 1 is on...but leave the right side blank/

Thanks that worked. But how do I make it so when I change maps and come back that that event doesn't happen again. Like say I obtained an amount of exp from using action on an item and went to another map, and came back. What if I wanted to make it so I couldn't gain more exp from that item?

That self switch method does make the action only available once, even after you leave and re-enter map.