Plenty.
A lot of unknowns here, so lets go with the basics.
ABDL for a sissy baby can be a lot about the power dynamic and humiliation, not regression, so dont expect the sissy to act exactly like a baby, and dont force it that way either.
How long the scene will last will limit what pays off. Enforcing baby behavior, like playing with toys and coloring in books, is a larger time investment than an evening. Think a weekend with time in between direct or erotic play.
Chastity is a thing for sissy babies, but it requires a bit of trust and getting to know the other side a bit.
Denial of an orgasm is something you should consider to open with. Keeping the sissy horny will keep them in sissy sub space.
Milking is part of anal play, so talk that out first, but if they are in for it, you can use milking as a substitute for their orgasm.
Spankings is pretty much universally loved by sissies, but the severity needs to be limited to what the sissy can take.
If the sissy is allowed to orgasm, make sure it is in the diaper. This can be achieved by letting the sissy rub the outside of their diaper, or letting them hump an object, like a teddy bear. Make sure to mock them for it while they are doing it. Get them to associate the mockery with their orgasms.
Listen to some Mommy Cloud videos on YouTube before hand, to give you an idea what tones you can use with the sissy baby.
There is also one video on YouTube about turning your SO into a diapered baby.
Kit wise, buy a pacifier, a baby bottle, some juice, and some baby toys. Make sure they make a show out of playing with them for you, at least for a while.
If you do have a full day or more, buy a Barney video, and make them watch it while you make lunch or do something else. Bring a book for yourself and read it during your own break, and make them play with baby toys in front of you. If they refuse, then do spank them, and make it sting a bit. Then ask them to play with the toys again, threatening another spanking if they refuse. Dont let them out of their sissy baby role for one minute.
Your orgasm matters more than theirs. It is part of the power dynamic, and they should value your orgasm over theirs, even if they dont. If they dont, then they need more training, which is your job.
There is also a question of what the dynamic between you two will be. Will it be strict, punishing and servile, or will it be loving, caring and gentle? Cuddles are a big thing for all babies, sissies included. Some babies dont get them, for various reasons. Sometimes, it can be because a Bull doesn't want the cuckold to get any attention. Sometimes, it is because the Care Giver (you) doesn't like the baby in a loving way. Still, cuddles is a big thing for all babies, but it is not universal.
Do you intend to play with the sissy baby again and again, or is this a one off date?