DIY dog booster seat for the car. Cut out two bigger holes in the back for the seat belt to go through and tie a leash to the top. Sew a cube shaped pillow for the interior and a slip cover with elastic for the top (for ease of cleaning) and you're set!
Smashed Peas and Carrots: Booster Seat Cushions Tutorial --- I might use a chunk of firm foam or ducktape the hoot out of an old phone book and then cover it. I like the idea of using a vinyl tablecloth.