Indeed. Since I quit smoking I miss the inarguable excuse (not just to others but myself as well) that smoking offered to leave a party, go outside, stare into the night's stars and just relax while pondering the universe and my own insignificance.
It's mostly empty, though.
I think you can always say that you need some fresh air and go out.
Taking a moment to relax and gaze at the stars or enjoy a coffee on your own just sitting there lost in thought is as good an activity as having a smoke. I really don't see people judging other people for it.
Or if you're actually looking for an activity not an excuse, just thinking about a interesting topic/problem and writing down the thoughts going through your head on your phone (or even better onto a piece of paper/notepad, no interruptions) can be an very satisfying activity I found out.
Really helps me to focus on whatever I'm thinking about too.