At checkpoint 5, slowly roll onto the lift then reverse off it as soon as it goes up. This will allow you to drop into the area below it, where the Squirrel is hiding.
After checkpoint 7, ride over the shipping container then stop on the other side of it. The doors should have blown open, so reverse into it and the side will fall off to reveal a Squirrel within.
Right at the finish line, bailout to launch your rider between the red and green containers ahead. You may need to wheelie then lean forward as you bailout to get enough speed and height to clear the containers, then your momentum should carry you to the Squirrel.
A Pretty Good Wall
This track has a multiple stage challenge to unlock the Squirrel, involving triggering three sets of fireworks. The first is underneath checkpoint 2, so bailout backwards on the next ramp to hit the trigger.
The second is just below the checkpoint 5 ramp, so again bailout on the other side to launch the fireworks.
The third and final trigger is beyond checkpoint 11 - after being launched on the platform, bailout and roll down the cliffside to find a ledge with fireworks on it.
With all three triggers hit, reach the finish and bailout over the line into the now open building to grab the Squirrel.
After checkpoint 3, jump to the next ramp then stop on it and wait for a series of explosions to go off around you. Roll backwards and drop through the newly created hole to a platform below, then avoid the hanging barrels as you ride to the other side where the Squirrel is waiting.
When you reach checkpoint 13, hit the ramp ahead then bailout and hold up on the left stick to push your character towards the background. If you've got enough height then you'll drop on a hidden platform with the Squirrel.
At the start of the track, reverse until you hit a switch on the rear wall. Next, you need to make it to checkpoint 4 without faulting - if you do, reset the track and try again. Just after checkpoint 4, a secret hatch in the floor will have opened up, so drop through it to find a waiting Squirrel.