On Grimm each week the main character Nick finds a weapon, a book or a potion that will coincidentally defeat this week’s monster. And afterwards it is filed away or lost, usually never to be seen again. I have only seen the first series but so far, nothing has returned. Blasted aussie TV keeps moving things around.
Dad’s diary on Supernatural ought to be ten inches thick with the information that the Winchester boys pulled from it; at least in the early series.
I've also been watching Arrow, the TV series and the fabulous Island where Oliver was lost for years, has at some point, crossed from plausible to beyond ridiculous. I only identified that as my issue with the show when I recorded the last episode. I usually fast forward through the commercials but I caught myself pressing the ff button during the island sequences. I can no longer rationally believe that the Island is lost, with the amount of traffic to and from it. Or that any areas of it remain hidden or unknown.
So I guess you have to use expanding plot devices carefully.