if you want to get the last badge just use your boost on the last hill to fly over the boxes.
Your upgrade scheme should be like that: buy wheels, fuel, transmission on max and 2nd lvl engine. after first run: max your engine and buy booster with weapon and ammo as much as you can. Second run: max your booster and rest for the ammo. Third run: on the last hill use your boost.
 "Earn to Die"){kind=icon}
 "Parking Space"){kind=icon}
 "Bomb's Vacation"){kind=icon}