You have a couple of options. "I'm not sure yet, what are YOU doing?" "No, I wasn't planning anything" (there is no need to go into further detail). "I thought I might go out"

Now, as for what you DO do? Have you thought of starting a new tradition for yourself? You could in fact go out, even alone.

How comfortable are you with being completely forward as in inviting yourself over somewhere? I've done it and it's easier than I thought it would be. Again, "I don't know but what are YOU doing? Gee that sounds great, what can I bring?" The person is either going to think you are joking which you can laugh along or they will think seriously and say that would be great. Yes, lots of courage but you never know.