Collect all of the Die-o-Ramas to unlock the Baby Crash costume.
To get Crash's skeleton costume you must find the worker near the stunt arena and buy the costume for 4,000 coins.
When you find Cortex on Mystery Island there's an owl shaped lamp behind him. Hit the body-slam switch and it will rise up. Enter the cave, and go right. Have a chat with thethe drone at the top of the island and shell out 2000 coins to get the costume.
To play as Nina Cortex you have to give her the keys at Midway.
To play as Crunch Bandicoot you must give him 2,500 at Midway.
On the title menu, hold L1 + R1 and input SQUARE, CIRCLE, SQUARE, CIRCLE.