Harvest Moon: Friends of Mineral Town Easter Egg - Double all profits made in one day.

Starting with Year 5, then every 5 years after that (eg: Y5, Y10, Y15, etc.) visit the Peak of Mother's Hill on Fall 10 between 6PM and midnight to activate a serect event called the Shooting Star Event. Make the wish to double profits (option 3). The day will end. You then have until 5PM to ship as many things as you can. When Zack comes, he'll double your profits for Fall 11.
NOTE: Fall 10 MUST be sunny, or the event won't activate.