I didnt think that you could get the spare tire option with the SS or cars with 20" wheels? My guess is that there is room for an 18" spare tire but not a 20".
According to this thread it is not an option for the SS
http://www.camaro5.com/forums/showthread.php?t=7914
As for the air and fix a flat the air is nice because if you dont have a blow out you can air up the tire and try to make it to a gas station. And it is handy if you need to change air pressure at the track.