Hard to prepare for the unexpected and not all needs are the same but my experiences have led to me packing the following .....
Fleece blanket (hospital blankets are more like tablecloths)
Fleece dressing gown - doubles as a blanket
Nail clippers
Silicone ear plugs (there can be lots of noise during the night)
Mobile phone and charger
MP3 player but use headphones
Diary and pens
Slippers
Pyjamas
Torch (flashlight in the US)
Trainers for exercise walks on the ward's quieter corridors
Watch that tells the time, day and date
Books to read
Spectacles
Underwear
Blunt ended scissors
Electric toothbrush and charger
Pain relief (don't rely on the medics assessment - but use responsibly)
Soap and face flannel