How about looking for recipes for vegan/GF breakfast bars? I am sure I came across some on the internet, but I just eat GF cereal so didn't really pay much attention to where I saw them. Think that might be your best bet for food you can eat in the car
Check out this page actually, a bit further down there is a section on muffins
http://glutenfreegoddess.blogspot.com/p ... index.html