Check the temps before you pack. If mornings and/or evenings are cool you may want the options of adding arm and leg warmers, and a wind vest, all very light layers to have available. A light jacket could also work on or off bike. I would also bring 2 shorts that you really like, and a bag to hang off the back of your bike in case they they aren't dry by morning from the night before you are. Terry wrapper skorts are great for off bike time, and take up almost no room in luggage. Likewise, a soap you can use on both your shorts and body saves room. Jerseys that would go with bike shorts for on bike use and also a skort for off bike use are also a thought. Why don't you want clip in pedals, it will make a big difference in effeciency. I think you should bring your own saddle, pedals, shoes and helmet. It will help make the rental bike feel more like yours. If it were me though, I'd bring my bike too!