Small chrome mirror should be standard imho; however, it wouldn't meet UK safety standards, so has to be a retrofit.
Just thinking off the top of my head: -
As for other mods - short shift kit, which is not a true short shift iirc, but rather a shorter gear knob shaft.
AeroMan and Kin have custom exhausts, as do others - Shooter's car had a Librands as do a fair few other Aeros.
Obviously stereo mods are common - iPod adaptors and better/more speakers being the main areas of improvement.
Heated seats - not a difficult retrofit
Simmons fuel filler cap - a nice change to the S1, S2 and S3
...I am sure there are many others but that is a start
