It's hard to retrieve coins and other things that fall into the little gap between the car seat and the door or the gear box. Here's a quick, DIY solution that costs a dollar and almost no time.
You'll need a pair of scissors and a foam pipe. Align the foam with the gap, and cut out a hole for the seat belt. Insert the foam and pull the seat belt clip out. Adjust the foam so that your seat is sliding back and forth easily.
Easy $1 Car Seat Gap Filler [Instructables]