I was just thinking about the Presidential Key Dipper was given and couldn't help but wonder if it would actually ever be used again. Not just that really, but I could easily see the twins amassing a fair collection of otherwise useful objects and wondered if we would ever see any of them in action other then the episode they are first found. An example could be with Mable's grappling hook.
Similarly with new side characters I guess, while Mabel's new friends from the Double Dipper episode undouptably will show up again (I should hope) I wonder how such characters like, say, Mabel's new pet pig will continue to show up. After all, an item could be hand-waved away just by being lost in some proverbial closet, but it wouldn't be that easy to to explain away a living thing.