I also had a lumpectomy and sentinel node removal. I went in one morning and went home lunchtime the next day. I took pajamas which buttoned down the front as advised by others but ended up staying in my hospital gown. I found it helpful to take music and headphones because I couldn't sleep at night. I was pretty drugged from the General anaesthetic so wasn't up to much reading. I found it useful to take my mobile phone so I could talk to and reassure my adult children who were interstate. A soft bra without underwire which did up at the front was useful too. It seemed to give some support to my breast. A note book and biro to take notes is always useful.
I wish you the very best of luck in your treatment. I have met so many wonderful nurses and doctors since being diagnosed with cancer. It's wonderful that we have such high quality medical care in Australia.
Karen