USA - Rights while driving

[trptamene]

I think I basically know how to deal w/ cops when approached on foot but I'd like to know more about my rights while driving. I know the cops are aware of my (& most ppls) ignorance and use it to their advantage.

I know if I commit a road crime I can be pulled over and contact with the police is no longer consentual. I know once I get pulled over they cannot search my car unless I say they can or they have a reason. What gives them a legal reason to search my vehicle w/o me saying it's ok?

One time SWIM was driving out of south TX & got pulled over by a police officer, he took swim outside the car and mentioned that he detected a faint odor of marijuana. Swim admitted he smoked marijuana and had some prior, but got rid of it all as he knew he was coming to a police check point. The officer proceeded to search the vehicle & swim is pretty sure he didnt ask. Was this an illegal act on his part, or did swim give up his right by admitting he had and smoked a schedule 1 drug at a prior point in time?
Also, when swim got pulled out of the car, did he have to do this or is the cop just asking him to step out of the car?

Maybe there is more info about this in these forum, if someone could pt it out would be appreciated.

I watch cops a lot and I see people giving up their rights right and left usually ending them up in bars because of drugs or something similar found. I want to be sure I have the upperhand when dealing w/ these guys.