Clothing:
I ride in my suit to the station when I am going to biz meetings.
I usually wear a wicking/wool T shirt and ride at a non-athletic pace so I dont generate any sweat. You can roll along to cool down.
Toe clips enable me to wear formal black shoes.
In cold, wet weather I use a pair of ultra-light pertex rainpants that pack up small.
I solve the layering issue by wearing an insulating jacket in winter. When I get into a warm building, the jacket comes off in one piece, no struggling with different layers. It is a different strategy to a long training ride but works.
Bike:
If I am travelling less than 2 miles I may not carry a repair kit.
You can make the bike more suit-friendly by fitting a (hard to find) chainguard , a clean/dry lube and the most puncture protective tyres you can find.
Accessories (lights/computers etc) have to be removed at every lockup so I minimize the number of removables. A Dynamo lighting system is bolted on and cannot be stolen.
The 2 lock system is good. A shackle + a cable take different tools. Lock your helmet using the cable.
There are times when a bus or taxi are better options.