This request interests me, I'll take a look at it for you and see if I can find you a simple solution.
Edit: I found a solution for you, using common events. The problem with this is, it can require quite a few common events depending on how many reusable items you have.
First you will need to create a common event and link this to the item, you will need to make one of these for each item.
As you can see it is rather simple, but having multiple of these can be hard to keep track of. The next part you will need to do is make a second common event, this one will be triggered on each map that you can get in fights with.
You only ever need one of these events, you can simply add a check and a variable adjustment to this event for each item.
This would be a lot simpler with a script, and of course with common events I can't grey out an item for use, just remove it, but this should still have the effect you are looking for, I hope.