The Baby Bjorn carrier was well used by my daughter and I, less so by my wife. But any carrier that you are comfortable wearing is fine, it is the getting out and about without a stroller which is where it comes in handy - you don't have to watch your shopping cart like a hawk as the baby is strapped to you. It made getting from Boston airport economy parking to the gate for a flight to Ireland with a 6 month old a breeze. Plus it is darn cute.

We also have their bibs, a bit bulky for taking places, I just strap it on to the diaper bag to my wife's annoyance, but great at catching a meal full of spills.

A small diaper bag, just enough to hold a few diaper, wipes, clean set of clothes, snack and a sippy cup, rather then the typically full size diaper bags which haul a lot more and can be identified as been suck from 50 yards / 45.72 meters. This is so you can be mobile with child.

Poop bags - there is probably a more technically term, but they are small blue bags that can block the stink of a babies diaper. You are not going to need these until they start on solids, but given their blocking strength they are clearly a by product of some military program. They come in boxes of 50 for ~$5, at BRU they are in a generic yellow/brown box. Because you can't just toss a poopy diaper in a public bathroom trash can.

Second car seat - sure with LATCH / ISOFLEX it is possible to move seats around a lot easier, but that requires thought, buy the second seat / seat base and get going.
Books, touch and feel books, flap books, board books, they are all good.

Breast pump - this enabled us give my wife feeding breaks and hence allowing her to get a solid 4 to 6 hours sleep. Plus I got quality time with our daughter.

I am sure there were other things, but these are they ones that stick in my mind.