I have visited St Yan a number of times, mostly in the days before France withdrew border police from there and many other airports. On this visit I stopped at Caen, both ways.
The airport is sleepy except for a big airline pilot training school, but even then not a lot is happening.
There is often nobody in the tower so you have to make the phone call to get your flight plan closed. I forgot and the search and rescue people telephoned the fire crew to check the plane had landed :) Often the airspace around is uncontrolled.
As far as I know there is no food within walking distance.