The one accessory I never hear people getting is an extra coil cover, but I did, and I'll tell you why. I find that dirt gets into my coil cover fairly easily, and so I have to remove it in order to get rid of the dirt. The coil cover is not flimsy by any stretch of the imagination, but it's not hard to imagine that with use, wear and tear, age, etc. it could get brittle or crack. Have you ever REALLY looked at the coil charging set-up? The coil cover has the "guides" that hold the charging clip in the correct position to charge. No coil cover and you can't really charge the coil. I tried it as an experiment, and I could not get it to consistently keep a charging connection without the coil. I mean, I'm sure you could if you rig something up, or use some tape or something. But I figured I'd just get a spare coil cover.
By the way, I wouldn't bother with the car charger. You can get an USB automobile cigarette lighter adaptor for <$10 at a drugstore these days. Just plug in your extra 3 way cord, and you're all set. That's what I do at least.
Rich