Supposedly, the best thing for absorbing odors is activated charcoal. You can get it in quantity from aquarium supply stores, it's used in the water filters of freshwater aquariums. Back when I was actively playing with fish, it was very inexpensive.
It's non-toxic, in fact the poison control centers recommend giving it to patients in some situations (depending on the substance ingested). It may take a few replacements of the stuff, if what you've got in your car is particularly nasty, but it is safe and efective. But it may be a bit messy on exposure to small children, so watch for that.
You may want to hit the underlayment/padding with a strong bleach solution to kill off any small nasty critters first, but that may be difficult at this time of year if you don't have a place to dry the interior out after treatment. Just put a fan in there to blow fresh air through with the windows down, if you can.
Alternatively, there's always the "park it in a bad neighborhood for a couple days and collect the insurance" option, but that's sort of a last resort. Although there is a chance of it being returned with a full tank of gas and a sympathy card, if things are TOO bad.
Just as a warning to everyone out there: I've decided to say "F**k It". I've got too much shit going on, so I'm dealing with everything by letting my sense of humor totally off the leash. I'm starting my radiation treatments this week, and I have to deal with it all somehow. If things start getting too weird, say something, otherwise, enjoy the show. -S