I've also heard from various sources about damaging an ignition system with too much weight.
I carry a lot of stuff on my
http://www.Countycomm.com 'airplane mechanic's' 6" cable keychain. This includes an Arc AAA, spare AAA lithium in a watertight geocache fob, ladybug, stainless 'peanut lighter' (also from Countycomm), and, in the summer, when I switch the body on my Fenix L2D to a P2D, a spare CR123A battery in a Wal-mart keychain pill fob. The keychain cable is much handier than dealing with split rings; you just have to check to make sure the knurled ring is tightened every so often.
This is what I do. I have my car key and remote only - on a quick release clip. I use a 'lobster claw', but there are a lot of different quick release arrangements out there. I would include some links, but my computer crashed recently, and I lost all of my multitudinous bookmarks.
It's just a matter of training yourself to get in the habit. As I use the remote to unlock the car, I'm unclipping the ignition key from the still closed keychain cable, and dropping the cable/heavier stuff in the beverage holder. As I start to exit the car, I reverse the process. Hope this helps. You might want to check out
http://www.edc.forums.com