If you go the Turtle's Paradise restaurant in Wutai they told you that they placed 6 flyers all over the world. If you red all of them you can earn a prize. Here are the locations:

1) Midgar Sector 5 Slum. Enter the house to the right and go upstairs to the boy's room, the flyer is posted on the wall.

2) Shinra HQ, ground floor. Go to the back of the floor (near the elevator). You can see it posted on a board.

3) Gold Saucer, Ghost Hotel. Read it near the entrance to the itemshop.

4) Cosmo Canyon, arms shop. Posted next to it.

5) Cosmo Canyon, Inn. Go up the stairs and then next to the desk.

6) Yuffie's House, Basement. Just before the room with the cage.

If you have red all 6 of these, go back to the Turtle's Paradise restaurant and talk to the owner (the guy behind the bar). He will give you a Power Source, Guard Source, Magic Source, Mind Source, Speed Source, Luck Source and Megalixir.