In my truck, I pick up the trash every few days (not much, just receipts, occasional food wrapper, water bottle, etc). My kids tend to leave more trash in my wifes car (they are in it more) and I make them clean it out every so often.
As far as vacuuming, every few months on both of them (I do bring my wife's car to a local carwash every few months and gets a little better interior detail).
I had a co-worker that was a total car slob. Had a Toyota Tercell that was full of trash. It was a 2 door hatch and the hatch and back seat area was full of trash, passanger seat was about 1/2 full, no way anyone could ride with him. He had roaches in his car, and we make him park away from everyone else.
As far as vacuuming, every few months on both of them (I do bring my wife's car to a local carwash every few months and gets a little better interior detail).
I had a co-worker that was a total car slob. Had a Toyota Tercell that was full of trash. It was a 2 door hatch and the hatch and back seat area was full of trash, passanger seat was about 1/2 full, no way anyone could ride with him. He had roaches in his car, and we make him park away from everyone else.