| In all seriousness, the best two Cooper S I've ever driven had pretty much NO extras.
BUT, if you like music, of any kind, I suggest either the hi-fi upgrade or an aftermarket solution, the standard stereo is pretty dire. The multi-function steering wheel, which includes cruise control, is a really nice feature that you don't miss if you haven't had it, but find hard to live without once you have.
Most other options are a matter of taste. Half leather doesn't give you much leather, so it's almost worth staying with cloth, or going full leather, if you go full leather, I think heated seats are a must.
Aircon has fiddly controls, so auto aircon is very nice if you like your driving comfortable and unfussy. The Sat nav looks great and works well, but for mapping a lot of people rate other choices such as Garmin higher.
MOST people however just expect a Cooper S to have the Chilli pack at resale, but that doesn't mean you HAVE to have it, but once you tick a few options boxes it can work out better value anyway.
I would always opt for the sports suspension upgrade on the S, it's firmer than the standard, but I still found it comfortable and compliant even on country roads, but if you're thinking of going aftermarket on the suspension, who knows. | 
