I remember an interminable winter when my kids caught every bug and virus going and we seemed to be housebound between December and March. We did do the country themed days - I made them passports which we stamped, put chairs together for an aeroplane, (they had not been on an aeroplane so liked the emergency exits etc spiel) to fly to the country, had food etc, flew home. We also did letter themed days - I think I really was at the end of my tether! - so on J day we had to eat J food (jam, jelly), do J activities (jumping, jacks), wear J clothes (jeans, jumpers) - I forget what else!
Pen and paper games - the one where you draw a head, fold it over so just neck is showing, pass on, draw a body etc. The one where you write something down that can be drawn, pass it on, that person draws it, folds over the writing, the next person writes what they think it is, folds over the drawing, the next person draws etc etc.
Telling a story a word at a time in turn. In my house this usually descends into the death of all the characters. "Once...upon....a...time.. there...was...a.....sausage....One...day....he...died." Hilarious.