Originally purchased for a jeep, I have found this repair plug kit by Safety-Seal to be invaluable. Repaired more car tires with it than anything. usually use it after pulling a nail and use the to to insert the plug rope. Never had to re-balance a tire after either.
The $45 kit is what I have along with a harbor freight 12v air compressor and a can of fix-a-flat. Threw away the red box and put all of the kit in a small zipper bag.
http://www.safetyseal.com/