The artist posted this on Christmas day. In Japan even more than in Western countries, Christmas is thought of as a couples' holiday. They also have the tradition of eating chicken for Christmas dinner. The implication here is that this girl is buying her Christmas dinner from a convenience store and she's embarrassed that the shopkeeper will be able to tell that she's single because she's only buying enough food for a single person.
You could read into the situation more, but that's the basic gist.
