breastpads, because you will soak threw all your shirts, definitely bf bras, keep a towel nearby incase you have strong let downs to where the milk sprays (I had problems with that) I'd pick up some nipple cream, I never needed it but a lot of girls I've talked to have had to use it, burp cloths, a boppy pillow makes it more comfortable. Learn different positions that way you can find what works best for you and baby. And just If you feel like giving in up, just know the hard part will pass and it will be so easy after that. If I think of any other materialistic items I'll let you know.
breast pads, nipple cream, a pillow or boppy.... I usually tuck a burp rag under my boob into my bra so that if she drools some out it doesn't end up all over me.... also a pump if you will be returning to work, or even if you're not, I have one for when my daughter doesn't nurse on both sides, or if I am away from her for an extended period of time
the first couple weeks honestly, between growth spurts and getting the hang of it it sometimes hurts, not gonna lie.....after that it's smooth sailing (altho growth spurts still happen and you get tired all over again)
The hardest part for me was learning when to switch to the other side, and how all that worked. I ended up giving myself over supply from not draining the boob completely, but I got it under control in a week or two and after that it was smooth sailing.