How do i make my room cat safe?

I have a doll collection on a shelf, books with Halloween decorated items. And my boyfriend has a lego collection by his bedside. I'm not sure where to start.. My cats want in my room but they have an addiction to eating or chewing plastic and other items.. Help?

Can you put the collections in an enclosed display case, where the cats can't get at them?

I don't have an enclosed display. Just a tall shelf with tons' of dolls Barbie sized.