I don't have this problem because all of the people that I am friends with that ride in my car do respect other people's property.
I mean occasionally someone will snack on popcorn or some sort of nuts or chips and perhaps have a drink but it's no big deal for me.
The two times something "horrible" happened, both drink spills, I had nobody to blame but myself
I put shit on top of my own hood roof trunk whatever (albeit not frequently) so long as it doesn't have anything that can scratch the surface and doesn't weigh a ton so that it dents the surface, who gives a shit?
Enjoy your cars.