I suggest upgrading the engine, tires, windshield and bumper first. Then go for body armor and fire arms. The last ones you should go for are the horn's and perception.
Its better to hit 1-2 cars then have a Mutated zombie on your hood so you don't have to shoot you windshield out.
When you know the chopper is coming trying driving on the sides so when it shows up above you you, it hits a sign before it can get in front of you.
Trying staying in the lane until the the jet comes around to do a bombing run, it throws it off.