If your sick of bringing half the sea home with you in the car you cant go too far wrong with the Frostfire Moonbag. I have mine nearly two years now and it has served me well so far.
The bag doubles up as a changing mat and you basically stand in the centre, take off your wetsuit and when your finished you pull the drawstring and your wetsuit and other gear are in a handy waterproof bag. Its pretty useful for changing at gravelly car parks like Streedagh; the padded base will save your wetsuit from tearing on the rough gravel as you try escape the cold in a hurry!! The tough nylon bag is hard wearing and pretty good value at about €20. The bag can be bought on Amazon or Magicseaweed.
Another option (and possibly a cheaper one) is a rubber bucket. It may sound crude but these buckets are very handy and sit nicely in you boot, keeping your wet gear from destroying your car. The buckets can be bought in most good hardware stores or thrift shops. I think I even spotted one in the back of Fergal Smith’s Relentless Van, so if they’re good enough for him they can’t be too bad!!