Pjs and a thin dressing gown at least two or three pairs as it can get sweaty in hospital.
I find that deeply unflattering xl men's tshirts are best for easy access to your arms and tum for injections, blood tests and blood pressure checks whilst keeping you well covered up.
I wear soft crop tops underneath as I'm not happy going completely braless and these shouldn't get in the way of any tests and are comfy to sleep in.
Something to keep you occupied when you are recovering/waiting-books, audiobooks are especially good when you aren't feeling your best. Don't rely on tv-in most hospitals you have to pay and they are rubbish, my local hospital doesn't have wifi either
so load your phone up with games and music etc before you go. (don't forget the charger)
Obviously a wash bag with hairbrush, shampoo, showergel, makeup toothpaste and brush and deoderant.
Nice things to eat and drink are good too especially squash because they like you to drink and water soon gets very dull and the tea/coffee might not be up to costa standard.