To see what extras ate available or still needed push the back button in your phone, or I think the treasure chest icon on the screen. Then go to progress log and scroll all the way right. Now the 5 easiest extras to get and the quickest order is.
1. High alt: as soon as u first take off from Arctasia, the first island, go right and keep hitting the thermals to reach the peak next to you. Just keep going in a circle to the right and eventually you will reach the top getting #'s 1 and 2.
2. Spear point: see #1
3. Crazy fast: after you get the above 2 dive towards the water. You will unlock it just before crashing.
4. Booster: fly around and go through one of the many red crystals.
5. Handful: collect 25 crystals. It only counts the blue, yellow, and pink ones. On the first island it is mostly blue so fly around until you get it. There is slot in the cave right under where you take off.