Wear whatever you feel comfortable in...you don't necessarily need to fork out on any special "cycling gear". Normal clothes is all you need, cycling is just another means of transport if you take it leisurely. I ride similar distance, just dress the same as if I was driving or walking it...for me that's usually high heels for work with nice skirt/summer dress. The only must have is my pac mac in my handbag - extra large man size so it keeps me covered, and is big enough to go over my nice wool coat in winter if need be. Also wear gaiters over my shoes in v wet weather - lighter to carry than spare shoes.