Tongue in cheek way of saying he saw methamphetamines in your pack of cigarettes. The clever part is that he uses the names of two Wu Tang artists Method Man (aka Meth) and Inspectah Deck (as in inspecting your deck).
a Gulfstream is a very expensive private jet. G4's are one of the most expensive ones. to give a comparison, G4 is the same in the private jet world as a Rolls Royce is in the car world. def a balla to fly in em!
CPT is an abbreviation for Compton, which is where Dr. Dre is from. LBC is an abbreviation for Long Beach, California, which is where Snoop Dogg is from. It just means the two are doing another song together.