What do you all do for car safety?

How scary! What about crash tested seatbelt harnesses like the Clickit or Roadie? Seems like those might be your best option given the restrictions you have.

They are custom made for each vehicle, so it's unlikely they would fit both old and new vehicles, unfortunately. The are well worth the price otherwise - well made, sturdy, and they can be left installed and still roll windows up and down with no issue.

I pray and drive carefully.

My car is too small for crates, and I am unimpressed with all of the harnesses/seat belts I've seen. For my next vehicle I should be able to go big enough for crates out of the crumple zone. For now, they just ride loose in the back seat.

Gage has a soft crate, but with his size he isn't likely to be safer in a hard crate, and one wouldn't fit anyhow. With a seatbelt he would still hit the roof in a rollover, so the soft crate seems like the only decent option.
The littles ride in a wire crate that is strapped in to the truck with luggage straps so it will hopefully stay in place in the event of an accident. I am looking for a hard crate to take its place but I have a size limit that I need to stay within and I need something that has a quiet door because I can't handle one rattling.

Both guys are crated in my Mountaineer. I have had a couple of friends get into accidents with their dogs in the car with them. The crates kept the dogs safe and that's a good enough reason to use crates in my car.

He has a kong harness with a seatbelt attachment
It has a chest plate and clips in the back

We aren't in the car enough (I don't have one) to really try to drag a crate in/out.

He sometimes will sit in the passenger seat at my feet