Paper cave: I think ceilings are underused for interior decorations. Would love to try some more colorful paper or plastic cones on our ceiling. At least in a small section. It would also be a great way to add too a "man cave".
Everyone gets a square with a quarter circle, this is the end result- could be a good ice breaker beginning of year activity. Each student decorates the square and includes their name. Nice way to decorate the bulletin boards in the beginning of the year!