If you're riding at night - wear bright clothing/hi-vis stuff and get some lights.

If not, just wear some older clothes, I usually wear a pair of track pants and t-shirt (t-shirt over a base layer sports vest if it's cold) - because I use a backpack, that insulates my back and I'm usually very warm due to my general warm body temp.

In the cooler climates, you will want a warm hat/do-rag under your helmet and some gloves and perhaps a scarf. Warmer, just get some gloves that'll prevent/help with road rash should you ever go down on the asphalt. Take or carry your work clothes on your off day, or in a pannier/backpack/bag and some babywipes/deodorant and you should be set. Rainy days will be messier without fenders, but so long as you have a dry, clean set of work clothes (including shoes/socks/underwear) then you should be set no matter the weather.

Good luck!