1) Talk generally about what people or things will be doing / will have done in 50 or 100 years.
Example topics: Work, The Internet, Food, Facebook, Music, Animals etc...
2) Write a letter to your future self in 25/50 years saying what you will have done and what you will be doing at that time.
3) Draw a time line 30 years into the future, Talk about what different things you will have / will have done / will be doing. (every 5 years)