Successfully complete the game to unlock the Army and Battle costumes for Regina. Successfully complete the game a second time to unlock the Ancient (caveman) costume.
Grenade gun
Successfully complete the game three times. The grenade gun with unlimited ammunition will be available at the start of the next game.
Operation: Wipe Out mode
Successfully complete the game with a time under 5:00:00.
Puzzle preview
When at a puzzle, before changing it, around push the button. Nothing will happen, but if you watch the colored lights they will turn on in the order needed to solve the puzzle.
Save ammo
There are some areas that you will only pass through once or twice in the entire game. Killing the dinos in these areas is pointless; more importantly, it is a waste of ammo. Use the weakest tranquilizer dart on it/them, and move on. This way, the bullets/shells/slugs/grenades are available when you need them. Once you get unlimited grenades (by completing the game three times under the normal difficulty setting), you can kill those dinos, without wasting ammo.
Shutters
Since the dinos can not pass through a shutter, use them to your advantage. Close each shutter after you pass them. This way, if a dino appears in that particular area, you can not be attacked (unless, of course, you are on the same side as the dino).
Alternate costumes...