The nooks and crannies of cars are just made to hold bits of leaves, the little paper thing that comes off the end of a straw, stray pennies, crumbs of whatever you were eating, etc. A household vacuum cleaner with the smallest and cleverest "crevice tools" that go on the end of the hose is a big help.
There might be some 12V car vacs now that provide both the right tools and a useful amount of suction but it isn't a market I'm familiar with.
Refraining from eating in the car helps even more. (Let's not even talk about smoking except encouragement to quit.) Food crumbs and bits of food wrappings just naturally make things worse. If you have kids, well, good luck.
Oh, yes, and good floor mats are a big help. The quicker they start to look dirty, the better the job they're doing! Frankly, I like the sport-ute ones that can actually contain about a quarter inch of water and mud and whatnot until such time as you can (carefully) lift them out and dump them. Better there than on the carpet...
There are all sorts of back-of-seat and console and inside-the-trunk organizers, so shop around and see what fits your car and your usage scenario. An organizer that you never use because it isn't quite suit the need is just more clutter in its own right.
Cheers,
--Joe