while the explanation about cocaine is accurate about that drug, i think he is actually high from smoking marijuana and is comparing this high to the fact that nose bleeds sometimes occur at high altitudes because of dry air
i have a Desert Eagle, which is a semi-automatic pistol. you load bullets into it with magazines or "clips" that slide into the handle of the gun. i have an extra clip which is already loaded, so i have approximately 8 more bullets available
to "push" means to drive, possibly from the fact that when you drive a car you are making it travel forward as if pushed. so, he is wondering why you doubt he drives expensive cadillacs (maybe because you're jealous).