Unlock Gold Card:
When you have card collection is 100% completed the Gold card can be found in treasure chests on F13.

Unlock Platinum Card:
When you have the Gold Card the Platinum card can be found in treasure chests on F13.

Below is a list of the 'Key To Rewards' items that you can get on your first playthrough (when you have completed the game they will change).

Megalixer:
Destiny Islands

Lionheart Keyblade card:
Traverse Town

Metal Chocobo Keyblade card:
Olympus Coliseum

Mushu Summon card:
Hollow Bastion

Thunder Raid Sleight:
Neverland

Stardust Blitz Sleight
Twilight Town

Warp(inator) Sleight:
Agrabah

Aqua Splash Sleight:
Monstro

Synchro Sleight:
Wonderland

Bind Sleight:
Halloween Town

Quake Sleight:
Atlantica

N/A:
100 Acre Wood

Beat the game once as Sora to unlock the Reverse/Rebirth mode where you are able to play through the story as Riku.

When you have beaten the game once the Theatre mode feature will become available. In Theatre mode there is an extra option on the 'Main' menu which allows you to re-watch any cutscene in the game.