I'm expecting my fifth baby currently. My must-haves are.....
Moby Wrap (or other wrap - they have breathable ones and ones where you can wear baby on your back when they're a little older)
Co-sleeper (I have Arm's Reach since I roll around like a fool and also have two dogs in my bed. I can lay right up against it and nurse in a sidelying position while I rest.)
Muslin blankets (I keep my room cold and like to swaddle my babies at night time only. I use the same blankets to cover myself while nursing in public and to cover the stroller if one of my babies/kids is resting in it.)
Rocker/Bouncer/Swing (Each of my first three babies would only rest in ONE thing without being held... so I had all three, although only one would get used with each child. My fourth-born liked all three, so thank goodness, you just might use them all.)
Receiving blankets (My babies are prone to reflux, so they spit up a LOT. Burp cloths aren't enough for some of the projectile vomits some of them have had. Nursing really, really helps with reflux, but my babies spat up any time they got a bottle.)
Baby mild castile soap (Read the ingredients on most "baby washes" - yuck! There are a few other "premium" brands with safe ingredients, though.)
Bac-Out (I run my diapers through with it every so often so they don't stink. I didn't know about it when I was CDing my oldest, and since I make my own laundry detergent, I added tea tree oil to one bottle of it and used it exclusively for diapers... It did keep the stink out and got them cleaner, but I don't like the smell of tea tree, either!)
A few other things I can't do without that wouldn't make a registry... I make my own all natural, cloth diaper-safe diaper rash cream (let me know if you want the recipe - I found it on a blog), but I've also used California Baby brand (which smells terrible and doesn't work as well, but it is comparative to "Desitin," which my sister uses on her babies, in my opinion). I use a teeny bit of baby mild castile soap in their baths (my 5-year-old now likes to shower, so I make him a body wash out of a bar of castile soap).