Not really, just whatever you think will see you through the day as there is a lot of waiting. So book/iPod/magazines whatever. Bear in mind though that you will have to leave your belongings for part of the day so unless you have someone with you to keep an eye, don't take anything valuable.
I was in overnight so slightly different but I've read on here that people took pyjamas and slippers to change into for comfort as there is so much sitting around. Or a dressing gown to cover up the hospital backside-revealing gown.
I took dressing gown and slippers. They gave me a nice hospital gown to wear. You need some sanitary pads for after. You will wake up with a hospital one in place. Some change for vending machine. My husband stayed with me in the bay whilst I was waiting and was there when I came back. But it meant he could go off and get a packet of crisps. Something to distract-book, magazine etc. At home you will need some painkillers. Would recommend a collection of DVDs. Spent the next day just watching them.