Easy way to get ontop of things.
How-To
Always keep a plank on you.
The plank can be carried ontop of the car if you dont drive like a maniac, or on a trailer with a box holding it down.
When at the destination, Simply rotate the plank to upright position and let it fall onto the wall, making a ramp you can do the basic half life crouch jump, to get ontop of the car and onto the ramp.
Good stuff are hidden on top of buildings, much worth.
Source: https://gameplay.tips/guides/5886-the-long-drive.html