Pilotwings 64
Warp To San Fransico
With this trick you can warp from New York to San Francisco. Start on Little States Island and select either the Rocketbelt or the Gyrocopter. Travel west from Central Park to the building with an open door. Walk inside past the N64 logo, and look for another door to exit. You'll find yourself in San Francisco.
Credit Goes To: Billy Hatch via IGN 64
 Warp To San Fransico
 Warp To Washington
 Finding The Birdman
 Stars
 Refuel Your Vehicle
 Get 100 On Jumble
 Hopper
Warp To Washington
In Florida, fly to the small warehouse. You should see a small opening. Enter it and check out the details. When you leave you'll find yourself in Washington! To return to Florida, simply re-enter the warehouse.
Credit Goes To: Ryan Senneker via IGN 64

Finding The Birdman Stars
Since the instruction booklet doesn't make any mention of where the stars are in the game, here are their locations:

Of course the star turns you into the Birdman suit,unless you're already flying the Birdman.
All of those,with the exception of Holiday Island, are nearly impossible to get without using the jetpack.

Refuel Your Vehicle
While there isn't a code to give you unlimited fuel, there are other ways to refuel your vehicles. There are two gas stations on the "Little States" island from which you can refuel. If you follow the road to the northwest from Cape Canaveral in Florida, you'll see a gas station on your left. Fly around in there until you hear the same noise you hear when you take off from a hopping pad; you need to be close to the ground. Also, near the nuclear power plant (in the midwest) is a little town. If you fly into that town with either a rocketpack or the gyrocopter you can get a free refill of gas by going under a little gas station roof! This helps you a lot if you are just exploring or are low on gas for a mission!

Get 100 on Jumble Hopper,mission 3
Jump between the building you start on and the building in front. You will notice a doorway on the building in front. Go through this into the Nintendo building and out of the other doorway. You are teleported to near to the end of the level. You can get 100 every time. It is difficult to get in the doorway, so I worked out an easier way. Aim against the opposite building so as you bounce into or close to the doorway. This makes it easier.