Long answer alert...
Nightie for the first night at least in case you still have a catheter in!
Big knickers (thing a good few sizes bigger than your regular size), if they fit you pregnant then they will fit after (you still have a bump after). Make sure they reach your belly button as if they are lower they can rub on your scar once the dressing is removed. Take black (to mask any leaks) and maybe 2 pairs per day in case you want to change if you do leak (bleeding can be heavy the first day or two, and increases when you feed, if you are breast feeding).
Tummy belt....do you mean those things that cinch you in and give support? You would need to wait a few days for something like that it would be too painful at first. Talk to the physio if you see one pre going home. You only want medium support (we used to recommend medium support knickers to women) as you want to use your muscles a little to get them back in shape. Total support means you don't use them very much. Our physios only recommended support belts to those with symphysis pubis dysfunction.
Peppermint tea is great for wind (most of the morphine I gave out was for pain from wind rather than direct scar pain! It can be quite sore.) Fennel tea is good too but works on helping your milk production.
Slippers or flip flops - up to you. You can wear flipflops in the shower which some women prefer when they are sharing (make sure they have a grip sole so you don't slip over!)
The usual stuff, feeding bras, dressing gown, toiletries, hair brush, sanitary towels (night time ones work just as well as maternity ones make sure they are for a heavy flow). Make sure any clothes you have are dark in colour so any breast milk leaks/blood leaks are hidden. I used to see all these women in beautiful white cotton pj's or nightgowns and then they were ruined by blood stains! Take a couple of snacks too. You can get hungry/thirsty when you are feeding and there isn't always something to eat on the ward. Lansinoh for your nipples (if you are breast feeding). You don't usually leak until the milk is in but a few breast pads just in case. Your ipod or something to listen to to block out noise from other people's visitors, or just to relax. Baby clothes too but there are lots of feeds on here with lists for that.
I also used to tell women to pack a small extra bag of baby stuff and clothes for you (sanitary pads etc) in case you have to stay a little longer (say the baby isn't feeding). Leave it at home by the door. Then your husband/friend can just pick it up and you don't have to worry about lists of clothes etc and you get everything you want. I remember a husband being sent home for more knickers and returning with 4 thongs...not too good for keeping big maternity pads on! hehe