Do the following to unlock each of the unlockables.

Unlockable	How to Unlock
Mega Weapons	Beat game once and enter challenge mode. Now visit a vendor to purchase Mega Weapons.
RY3NO	Beat game then it should be in the first vendor on Planet Florana.
Sketchbook	Beat Game once then should be in Cinematics menu. Press L1 or R1 to cycle through.