When you get your admission letter they will list the essentials they need you to take. You can then just concentrate on the things you need to prevent boredom.
They'll bring round jugs of water regularly but it would be worth taking in a smallish empty bottle that you can top up and keep in your cabinet in case they forget.
Possibly pen and paper. I was in once for an oral biopsy and couldn't speak afterwards. I also had enormous trouble getting painkillers so maybe some aspirin or paracetamol but make sure you tell them what you are taking.
Definitely earplugs as suggested. The ward can be very noisy. I finally got to sleep one night only to be woken at midnight to be asked if I wanted a sleeping tablet. Again, I imagine things have moved one.
Have you got an iPod or can someone lend you one?