To my mind, to miss something is to long for that thing; from what is gone before.
If that's the case, then I miss very few things indeed. I don't even miss my happy childhood for I have no urge to be a child again; nor do I want my childhood to catch up with me today. Now that's quite an interesting thought. Never quite thought of it this way till now.
I guess if I long for anything, it must be what could have been; and as what could have been never was, I couldn't possibly be missing it. So suppose I was ... am, "missing" something, that thing must be, could be, should be (in) the future. Alas to reach it!
