Nipple shields. These are somewhat controversial in the breastfeeding community, I guess because sometimes they are associated with nipple confusion. Ask me if I care, though. I think they are the best invention since sliced bread and they absolutely work. This little thing saved our breastfeeding butts the first few days home and even though we don't need it now, I am a huge huge fan.
3. Coconut oil. This isn't a baby product, but it swear by it after being a mom for all of 13 days. Just before Charlotte was born, I read that putting coconut oil on a baby's bum makes the first newborn poop (meconium) not quite so sticky. It totally worked! Changing Charlotte's first few diapers was fairly easy because the coconut oil acted as a barrier and kept her smooth. We are using it at most diaper changes now, simply to prevent diaper rash. Seems to be working.
4. Baby hats. See number 1. Our little lady sleeps every night with a hat on her head. Like her daddio, baby likes to be warm.