OK let me say up front I hate the ACLU and what they stand for since they refuse to honor ALL of the Bill of Rights.
That said, I recommend watching this video they produced.
The difference from reality is that the officer would have seperated the individuals, not kept them together and allowed one who obviously knew his rights to speak, and attempted to find a weak link. The other guy or girl would have been a weak link in that video, and probably consented or given information that gave probable cause.
That is the normal tactic. They especialy like to seperate nervous or unconfident individuals from the group and get them to give information that allows them to proceed. Often females will be targeted, and if they have children threatening to take them away is a common tactic to get them defensive and cooperative. The irony is if they did do something illegal, by cooperating and incriminating themself or others they are making a case for taking thier children when none could have otherwise been made.
They try to get emotions high in any vulnerable individual, and fear high to cloud judgement and get someone to say something to gain probable cause through self incrimination or a waiving of rights.
Another tactic is for an officer to assume some logical information and say it came from another member of the party, or make something up and make it appear the other guy/girl is putting the blame on the guy being talked to. If they can get him defensive he might incriminate himself or the other person believing others of his group are turning on him, giving probable cause or a confession by actualy saying something about the others or himself. Once they have even a minor confession they gain probable cause.
Once anyone gives any incriminating information on either themselves or another person, probable cause has been met.
Further even though that video uses people who are actualy breaking the law, there is many situations where even when the law is not being broken not giving the police extra options is smart.
For example in CA there is assault weapon laws. If you have a CA legal AR for example, and the officer determines it is an assault weapon incorrectly, even if it is not, it could still result in charges requiring a lot of expense and time to eventualy prevail. At the minimum that could result in arrest, before sorted out by a supervisor, charges dropped by the prosecutor, or you prevail in court. It could cost you money to post bail, time missing work, impound costs for the car which would likely be towed, and having to explain to work or family what happened and why you didn't show up.
Many normal items could be considered something they are not. Have some reloading equipment? Perhaps the officer considers it bomb making material, or the powder measure/scale drug paraphernalia for weighing and selling drugs. Perhaps one of the magazines can have a single extra round smashed into it exceeding legal laws, or perhaps they say your legal high capacity magazines are illegal. They could say the barrel is too short on a firearm with a permanent flash hider etc installed that makes it legal.
There is many non firearm related items that can have the same result in the officer assuming they are something they are not, though since this is a firearm board I will limit it to firearms.
So just because you are not breaking the law does not mean you have nothing to hide. You may in fact have things to hide you do not even realize, even legal things that could cause you a lot of trouble, legal costs, and time.