Alternate costumes:

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.

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).

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.

Get the third Energy Key Card early:

Before leaving the jungle, you can retrieve the
card from the shallow stream. This way you will
not have to make a return trip after finding out
that it is needed.

View Ending 3 without agreeing with Rick:

It is possible to get Ending 3 after agreeing with Gail. When the game prompts you to agree with Rick or Gail at the end of the game, choose Gail's decision to go after Dr Kirk. After the intermission sequence, go out the main door of the room. Go across the room to the double doors that lead to the Central Stairway. Once in the Central Stairway, if you have the infinite grenade gun, kill the two dinos in the room. If you are low on ammo and do not have the infinite grenade gun, try to run around them and not get hit. Go all the way to the end of the hallway to the Security Level A door. Go through that door, which leads to the Port Transport Passageway.
Get on the slider and go across to the other side. When you get there, get off of the slider and go through the large sliding door to the Heliport Transport Passageway. Get onto the new slider and go across to the other side of this area. When you arrive, you should see a large door in the middle of the wall in front of you and a small Security Level A door to the right of it. That door leads to the Underground Heliport. Enter the Underground Heliport through the Security Level A door as the Large one will not open. Walk forward until you see a sequence that shows the helicopter. When you regain control of Regina, exit the Underground Heliport. Go back
across the slider closest to the Underground heliport. When you arrive back at the other side, do not go through the large sliding door to your right. Go through the large door in front of you. The room you enter is the Transport Passageway, not the Port Transport Passageway. Be careful, as a dino will attack you. Kill the dino, then walk forward until you reach the Security Level A door that is on the right of the screen. Enter through that door, which leads to the Special Weapons Storage. You will find Gail and Dr.Kirk. The intermission sequence will take you back to the Underground Heliport. When it completes, go back out the door to the Heliport Transport Passageway. After that intermission sequence,
kill the T-Rex. When he is defeated, Ending 3 will play and you have successfully viewed it without agreeing with Rick.