I'm going to arbitrarily decide that footwear counts as being on-topic for this thread. I have a nice pair of waterproof hiking boots that I wore just enough to break in and then stashed in my car kit. With my bad back and exceptionally flat feet I'm dependent on custom orthotics to be able to walk any distance. That means only buying shoes that they'll fit in, and it also means that I have an old-but-still-good pair stashed with those boots. Footwear is rounded out with a pair of Under Armour socks (try them, you'll be glad you did) and some wool socks.

My car kit has a pair of quick-dry pants that are marginally acceptable for the office. I do have an inexpensive rain suit in the car, so I could wear the bottoms to get some degree of protection from snow as well. Skivvies and a belt round out this area.

I'm more well-prepared North of the equator. I've got a short-sleeve T-shirt, a heavy long-sleeve shirt, a heavy fleece jacket, a sweater, a light parka, my favorite rain shell, the upper half of my inexpensive rain suit (it's been handy to have both on several occasions), a scarf and ski gloves.

This kit was put together at minimal cost other than the boots. I bought a cheap duffel bag that's held up well in my trunk. The clothes are largely old, several pieces come from a former employer with their logo on them.