Check this site out, what a neat idea...I'm not making mine for the car seat but thought it would make a wonderful wrap for baby, even maybe put a velcro strip on it to keep it closed, or one could put a pocket in towards the bottom where the baby's feet would go...the ideas are endless...
http://www.imperfecthomemaking.com/2...-blankies.html
I have already cut one out tonight...so cool. one word of advice, the straight lines on the pattern, should be more of a curved one, as for the corner I used a plate to make the semi circle.