If you need to refuel and you're in the "Little States", go to the area around Atlanta. Just look and you should see a gas station. Land and go towards the building. Your gas should be refilled.
Get 100 Points 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 the end of the level. You can get 100 every time. It is difficult to get in the doorway, but if you aim against the opposite building you can bounce into or close to the doorway.
Holiday Island: Under an arch off the side of the island. Touch the star to recieve Birdman for Holiday Island.
Crescent Island: If you fly at the edges the whole time, you'll see and alcove. The star is inside the alcove. It's a tight squeeze in the alcove, so fly carefully!
Everfrost Land: You first have to fly all around to find the two waterfalls. And the caves. The caves are in or around the waterfalls. Fly in the waterfall on the right CAREFULLY! And when there is no more forward to the waterfall, look down and go SLOWLY down the hole.
Little States: Look for New York, and fly to Central Park, the star is in Central Park (the vehicle recommended is the Rocket Belt).