Wow, good question. Depends on the month. May can be chilly, so pack sweaters or sweatshirts and fleece. June is getting nicer but nights are cooler, maybe you can even bring out the shorts and t shirts. Ah, July and August. Perfect weather. You can wear your summah clothes, but have a jacket ready for when the sun goes down. We are a peninsula so sea breezes give us the natural air conditioning the city folk come here for. September is perfect sleeping weather. October can be cool (see May). If you want to look like a local, just where your WICKED SMAHT t-shirt, it goes with anything.
What you bike in is somewhat personal. People who bike a lot have very cool bike shorts with padding in all the right places. They also have colorful bike shirts that wick sweat and have a pocket in the back for your water bottle. For the rest of us, we tend to wear what we would if we were walking - t shirt, shorts or light weight pants and a jacket. Pants are the big issue, you want them to be snug around the bottom so they don't get caught in the chain. Some people like leggings or tie the bottom with a velcro strap. If you have wicking tops and jackets it makes for a dry day if you sweat going up hills. Please put sunscreen on ahead of time so you don't slip on your handles.