Make your own window cling decorations. Mix glue with paint/food colour then paint it on to a cookie sheet. They have to be pretty thick. Once they are dry (which will proably take a couple of days) you can peel them off and they should stick to your windows.
Also joke spilled drinks are fun. Colour your glue, I've done strawberry milk or coffee. Pour you coloured glue into a plastic cup then over a cookie sheet tip it onto it's slide, letting some of the glue spill into a puddle. Add a plastic spoon or straw to finish the effect. Again it will probably take a couple of days to dry.