I know a guy who commutes everyday to work with the slightly baggy mtb shorts and it works great for him. I would suggest investing in a nice backpack like the waterproof ones Ortlieb makes. The "cool" bike commuters at my campus wear as little bike gear as possible, but they usually take the bus when the weather is less than perfect! If you have a nice backpack can bring some extra clothes like socks, rain jacket, etc. I tried riding my bike to school last year, in what I thought was light, in jeans and had to sit through 2 lectures in soaking shoes and pants. Fenders and some protective glasses are nice for road grit and rain too.