For a Relative Clause activity have the students write a basic sentence on a piece of paper. Then they pass the paper to the left and write a relative clause that will add more information to the main clause. They keep passing their papers to make long funny sentences. Teenage and adult learners really enjoy this activity. For example:

A black cat walked across a street, (pass to next person) which was only a block from my house, (pass to next person) which is on the edge of a forrest, (pass to next person) which is haunted by the ghost of Mary Parks, (pass to next person) who had a lot of cats.