I feel like "System" is a bit of an extreme term. "Sensible" also means natural. Like, either they go on the kitchen counter, the dining table, or my desk, or occasionally the arms of the couch usually because those are the places that have space to put things like phone/keys/etc when I empty my pockets.

The only considerations are: Is the place convenient (read nearby when I'm likely to be putting things down)? Are they a flat and stable surface?

That's it. I feel like if people don't make those sorts of considerations surely they are just dropping shit on the floor