I have a cargo liner for the boot (it may be called a tray). When I first got one for my e53, I thought it was weird because it was so thin and light (I was expecting it to be like my rubber mats), but I came to like it that way. I got one for my 35d, then my x6. Carry mulch, rocks, beach stuff, or whatever and not worry about having to vacuum out your cargo area later.

I'm a little anal about wet and/or dusty dirty things getting on my carpet. That cargo liner once saved me from a chemical spill. I can't remember what it was because it was probably 5 years ago, but it was nasty.