If you have some scrap wood, zip one together with some deck screws. Here's mine, very simple and much more effecient than the other monster boxes and powerpanels I used to lug to the field.
http://members.cox.net/spad/pics/flightbox2.jpg
http://members.cox.net/spad/pics/Tattoflightlinebox.jpg
I also carry a simple tool box in my car that is full of repair stuff, more props, plugs, cleaners, small hardware...you name it...but 9 flying afternoons out of 10 I don't even need it. This simple box makes life easy and hassle free on the flight line.