One thing I haven’t really used (that I thought I would use all of the time):
Moby Wrap. It was really hard for me to put a floppy newborn into the wrap. I’m going to try it out again in a few weeks (and with a different way of wrapping), but I only tried it twice and didn’t care for it.
Things I thought I wouldn’t use but use frequently:
Baby Monitor. I didn’t register for one, but we purchased a $7 monitor the day that we moved Adeline to her nursery (6 weeks old)
Pacifier. I was kind of anti-paci before baby got here- but she really does love sucking on things, and since I don’t want to be a human pacifier, her WubbaNub has been great. She also hasn’t quite figured out how to keep her hand/thumb in her mouth, so a paci helps to calm her down when she’s frustrated
There you go- my list of things that I wish I had known before baby arrived!