I've only been arrested once (so far. lol) and somehow my money disappeared. While exercising your rights might cause you more trouble, that is the price of exercising your freedoms. You may lose them in the short term, but keep them in the longer term. That is how these nanny states grow. We are scared of having confrontations with the police, so we give up our rights. Then many of those same people complain about losing our rights.
Another example is a guy that purchased old cars, restored them, and sold them for profit. (As best as my memory tells me, anyway. Whatever the specifics were, he traveled for his business legitimately.) Because of the nature of his business, he carried a lot of cash. Many thousands. People won't take out-of-state checks and private sales preclude credit cards. Cash talks.
Anyway, he got pulled over for a light out or something very minor. The cop was nice and asked him some questions. One of them was if he carried cash on him. The driver said he had a large sum of money. The cop was thinking drugs, so he began an investigation. Eventually, the cop decided he should confiscate the money and did.
Normally, when you are suspected of a crime, the burden of proof lies with law enforcement. With confiscation, that is reversed. The burden of proof lies on you! In my opinion that is illegal, but that is the law. Anyway, the guy lived out-of-state, so he had to travel back and forth to attend multiple court hearings. This ate up thousands of dollars- most of what the cop legally stole- I mean "confiscated". The last I heard he probably wasn't going to get reimbursed for attorney fees, court fees, etc.
As far as valuables, depends on the size and amount. If it is long and skinny, you could stick it between the dome light and headliner. You could create a false bottom on your center console if you wanted to get fancy. Don't hide your stuff in flour jars, cereal boxes, and the like; that is a common hiding place and thieves will tear those open. Money in books is a bad idea for the same reason. Sowing money in curtains is also a bad place for the same reason. Just to be safe, I am going to state the obvious in case you accidentally might: don't post what your valuables are.