Crash Bandicoot Warped Demo: From the Load/New Game screen
Hold:& Press
This is documented in the US version manual but I have heard that it is not in the PAL version manual. The Crash demo DOES NOT exist on the Japanese version, instead it comes with a separate disc with a demo of Ape Escape(Saru Get You!).

99 Lives: From the INVENTORY screen

Open all six home worlds: From the INVENTORY screen