Concerning consent to search, you can search the area specified. If I ask, "Can I search your car?" And you say, "Yes." Then I get to search the car. Thats every part of the car, and not limited to anything.
If I say, "Can I search your trunk?" And you say, "Yes." Then I can search the trunk, and thats it.
Concerning searches based upon probable cause, it depends on what it is that gave the probable cause, As it stands now, if there is an odor of marijuana, I can search pretty much the entire vehicle, whereever the item could be reasonably held. You can't tell an officer "NO" to a probable cause search.
Concerning searches incident to arrest, it has been recently upheld that any search incident to arrest of a vehicle has to be in compliance with searching for specific evidence in refernce to the crime that you have probable cause to arrest them on. So say during a DWI arrest, I can search the vehicle for open containers of alcohol, and I typically search for receipts for purchases from local bars with a time/date that match up reasonably to the time I am arresting them at. Although I typically find these in their pockets when I search them, which is allowed incidnet to ANY arrest regardless of looking for evidence or not, because it is a safety concern for us to transport an individual who we don't know if they are armed or not, not to mention it is a felony to bring controlled substances into a jail.
Personally, I don't see any search laws to be too restrictive. Most laws concerning the search of vehicles are not constrictive, as most of the time they fall under the "plain touch" doctrine (this includes smells, and even the feel of an item when doing a "frisk" which is a totally different type of search under Terry v. Ohio), and the fact that you do not have a reasonable expectation of privacy if you have items laying out in a vehicle that are not stored away in a trunk or enclosed compartment.
There are a vast majority more restrictions on searches of residences. None of which I do not agree with. You have a high level expectation of privacy in your home, and even probable cause is not always enough to justify searching a home, as you have to be able to articulate a reason why the time frame for obtaining a warrant would cause a loss of the evidence, when for most situations you can post an officer on either side of the home and lock down the residence until the warrant is obtained.
As far as searches for blood, warrants are not too time demanding for most items, DNA is always gonna be there. However, I do not have a problem with NC's law regarding warrantless searches for blood in DWI cases. Alcohol is elminated from the body in a timely manner, in order to preserve the evidence it is important that we obtain the blood quickly, not 4-6 hours later. As in that amount of time one would lose a BAC amount of .06 - .09, which is just about losing enough BAC to not be impaired anymore. As long as an Officer can show they had probable cause to believe the individual was impaired by an impairing substance, then I don't see why the search cannot be made without a warrant. However, with that said. There are restrictions. A. The individual needs to refuse voluntary chemical analysis. B. If Im right next door to the magistrate's office, there is no reason why I can't obtain a search warrant for said blood which may take about 10-30 minutes.
Does that answer your question?