If you use paper towels, when you're done with the roll, just take it and stuff it with some of the plastic bags you get from everywhere. Stick the roll under your car seat and you're set for next time! I suppose toilet paper rolls would work as well, you just can't fit as many bags in it.
That's what works for me this week! Want some more great tips? Head on over to Rocks In My Dryer for many more!