I Don't Know
Yet.
Instead of saying IDK (I don't know) to a question, you can say IDKY so your friends at least have some reassurance that you're going to make the
effort to answer the question in the
future.
Sam: "Hey Tommy, are we on tonight?"
Tommy: "IDKY" (This most likely means that Tommy will eventually tell
Sam whether or not they're going to hang out. In this case,
Sam has the reassurance that he should get the update at some point that day.)