Without side tracking this discussion too much, If I get pulled over for speeding, or some other arbitrary infraction, and a law enforcement officer asks to search my vehicle and I clearly say "No, Officer, you may not search my vehicle" (You can't refuse a search of your person), and they do, I can assure you that they will be naming that town "Grandnational007ville" in short order after my legal council is done with them.
Police cannot create "probable cause" when there isn't any. And believe-you-me, I've heard it all: "You're vehicle matches the description of a car that just left a bank robbery! Mind if I take a quick look inside so you can be on your way?"
Of course every situation when contact with law enforcement occurs is different, and people get themselves jammed up, when they could otherwise be driving off with nothing, a warning, or a ticket. You need to weigh "but muh rights!" with "will I be able to just drive off after the officer realizes I'm a normal, law abiding citizen, going about their mundane business" with "did I forget that I might have (or knowingly have) contraband in the vehicle, and the the nice officer will let me go for being honest with them (the latter is NEVER the right answer...)
My humble advice? Don't have anything that could even remotely be considered "suspicious" within view of your vehicle. Carrying a substantial amount of cash? Keep it in a lockbox in the trunk, with the receipt from the bank. And travel with a discrete dash-cam that records interior audio if you're extra paranoid. Most modern vehicles now come equipped as such, and they are password protected if you are REALLY worried about corrupt leo's tampering with it.
It's not as sexy as some other alternatives, but drive a newer, non-descript vehicle in good upkeep and the interior not filled to the roof with garbage, obey traffic laws, and be polite should you come into contact with leo on the side of the road. If you do the above, chances are 99.9999999999% you'll be able to peaceably travel wherever you want, with whatever you want, and not get hassled by "the man".
Safe travels.