I would add to all of the great suggestions (couple of these may be slightly repeated from earlier posts) some sort of "dead pedal" , even if it is just a lip on the side to rest the edge of your clutch foot on for longer drives.
Possibly offer a couple of gauge cluster packages that include a better fuel gauge, rear tire pressure monitoring, temp, etc.
Maybe offer the standard long exhausts as is and another short pipe version that is a bit meatier.
