Hi Kirsty
I would echo what Peter has said because I also did this trip in October (2014). Definitely take a couple of sweaters because it can be bitterly cold, especially when the pollution makes the cloud cover thick. If you are lucky and have blue skies, as we did in Shanghai, it can still be t-shirt weather but I would always have a pullover handy.
In terms of what to carry, most of my group had small day-sized back packs. Be aware that in some places, particularly Tiananmen Square and the Forbidden City, you will have to go through airport style scanners and bag searches before you are allowed in. Be careful not to have any lighters in your bag as they may be confiscated as, bizarrely, sometimes are umbrellas. At the airports you will also find they are very picky about batteries and may make you take the battery out of your camera to be scanned separately. (Oddly, they don't seem to be so worried about needles and syringes - my medication was waved through without a second glance!)
Happy to help if you've got any other questions
All the best
Mandy