Kingdom Hearts Postcards
There is a side quest located in Traverse Town which requires you to collect 10 different Postcards and to send them out via the mailbox located in the First District. It doesn't matter which Postcards you turn in or which order - you'll be given prizes based on how many you turn in and that's it. If you're curious what the prizes are check the bottom of the page!
Otherwise, here's a list of all 10 Postcards and how to acquire them.
Postcard 1: Attack the Ceiling fan in the Item Shop located in the First District
Postcard 2: On the Accessory Shop's roof located in the First District
Postcard 3: The treasure chest on the awning in front of the "Boots and Shoes" store located in the Second District.
Postcard 4: The Blue Trinity Mark in front of the cafe which is located in the First District.
Postcard 5: Behind the Accessory Shop there is a blue safe, it's inside (First District)
Postcard 6: This Postcard is located inside a small pot on a shelf in Geppetto's House located in the First District.
Postcard 7 & 8: In the Third District cast Thunder on the broken wires. Then go to the Gizmo Shop in the Second District and press all three of the buttons on the top level. Then examine the clock in the room.
Postcard 9: Behind the post on the wall in the Item Workshop located in the First District
Postcard 10: Outside the Gizmo shop you'll want to climb the ladder to reach the roof. Jump across the rooftops and you'll find an opening which leads to the Third District. When you zone in you'll be able to use the Lock On after defeating the enemies to target a Postcard.
As promised, here's a list of all the prizes you can get from mailing the Postcards. Prizes 9 and 10 both are permanent increases to your Power and Defense.
Postcard Prize 1: Cottage
Postcard Prize 2: Mythril Shard
Postcard Prize 3: Mega-Potion
Postcard Prize 4: Mega-Ether
Postcard Prize 5: Mythril
Postcard Prize 6: Elixir
Postcard Prize 7: Megalixir
Postcard Prize 8: Orichalcum
Postcard Prize 9: Defense Up
Postcard Prize 10: Power Up