Oh... a MUST have for your car - wheel spinner knob
I looked at one of those several years ago for practical reasons and was informed that Insurance Companies considered them a modification which could affect your premium and if you had one they had not been told about in the case of an accident they could refuse to pay out.
Which also raised questions about whether our beloved DVLA consider them a modification, in which case you need to notify them as well.
Subject to the above they are legal for the disabled but I'm not sure about everybody else, a lot of truck drivers seem to be using them.
I did try one for a couple of days but found that in my case it got in the way more often than it helped so I took it off.