Journey by Stephen Clark  
    to Ridgetown

You wonder what you can do with a blank piece of paper. Then an idea hits you -- you grab a pencil from your pocket and begin to write:
"Dear Future Me:
    Hello, I am you from the past -- that is, I'm actually from the future but I traveled back in time from 1999 and now I'm here in 1965 and I'm writing this letter to WARN you about enrolling in Ridgetown college of TAFE. Do not enrol in this TAFE college in 1998 as you will be accepted into a much better course elsewhere and then you'll have to go to all the trouble of cancelling your enrolment. Oh, and here are the names of some horses who will win the Melbourne Cup..."

After you finish your letter, you give it to a well-known courier company with the request that it be delivered to your home in 1985.
    Your other self receives the letter in 1985 and takes its advice. You have succeeded in preventing yourself from enrolling at Ridgetown College of TAFE. Therefore this whole mission was unnecessary and you have destroyed the time-continuum on which you were existing -- but don't worry, you still exist on a different time-continuum and you have no need for TAFE college as you have become incredibly wealthy from winning bets on horse races.
The End