Get Island JackIn adventure mode go to danger island. when you get to the jungle go below the trees. when you see a giant snake wrapped around a tree branch near the end on the left side of the jungle shoot it and you will get island jack
Get prof. gutenburgGo to adventure mode and go to torpedo run there will be three subs on yor radar one of them is a yellow sub with prof. gutenburg on the front shoot two torpedoes at it and you will unlock prof. gutenburg
Get Andre LaToiletteIn Bigfoot Mt., when you start in the beginningof the level you will see a house on a hill. Infront of that house is a snowman, shoot the the snowman and if you shoot enough it will say you have unlocked Andre LaToilette.
Get Sheik Abdoul (the Arabian man with the rocket powered flying carpet)In the Cave of Blunders, you start above a Arabian city; in the center of town there is a small area (with pillars) where Sheik is being bullied by a palace guard. Kill the guard to get Sheik Abdoul.
Cactus RoseIn the beginning of Coyote Canyon on your right will be a town.In that town there will be a girl being hanged. Free her by shooting her and it will say you've unlocked Cactus Rose.
Get Sammy WasabeGo to monster isle. Shoot a ninja by the shrine in the middle of the jungle. If you did it right it the guy will say "you unlocked sammy wasabe.
Plane tricks.When you hold the triangle button and flick (or hold) the analog stick/directional pad up, down, left or right. (regular plane controls) You get...
triangle + up = "Dive Bomb" (pull up to stop the dive bomb when you desire)
triangle + down = "Somersault" (you use this in the mini game "Torpedo Run". You can't cancel out of the somersault when it's going. When you are accelerating you do a big one and a small one when not accelerating)
triangle + left = "Left Barrel Roll" (it will make your selected character do two rolls when you do this. When you hold the analog stick longer the left, you do a longer barrel roll. You'll automatically stop at a certain time when you can not barrel roll any more. It sort of works when you want to stop doing a dive bomb except that you continue going for one or two rolls then stop.)
triangle + right = "Right Barrel Roll" -see "Left Barrel Roll" description-
When you hold the L1 or R1 or both buttons and turn in the direction you want (left or right); you'll make sharper turns.
L1/R1 or both + triangle + down = "About Face" You turn around and fly in the other direction you were flying.
This is good to use if you accidentally go the wrong way. Holding L1+triangle+down makes a slow "About Face" You stay in that one spot and turn slowly (which wastes time) if not in Torpedo Run.
Holding R1 plus the other buttons make a fast "About Face" but it still takes longer.
Using L1/R1 plus the other buttons will make the best "About Face" you can do. So I recommend doing L1 & R1 + triangle + down combo.