Two bassinets/cribs-I know a lot of people put their twins in the same crib, which is great, but I could only do that for the first few weeks. My kids just don't hold still and they wiggle like crazy in their sleep, so two cribs for us was a must. I had them in bassinets for the first 5 weeks and I had two of those as well.
Bouncer and swing-personally, I did not find it necessary to have two swings and two bouncers. We didn't have the space in our small 1-bedroom apartment for two of each. But I found that having one bouncer and one swing worked out great. I always said if it ended up that oth of them liked the swing, then we'd go buy a second swing later. You don't need to have two of everything.
Two car seats-this one is pretty obvious. Of course you're going to need two car seats. I highly recommend going with infant carriers that you can remove from the car because it's borderline impossible to carry two babies at the same time to and from the car.
Spacious vehicle-you might think you can fit two rear-facing car seats in the back of your little sedan. And maybe you can, but good luck fitting anyone taller than 5' 7" into the front seat. And don't even think about trying to fit a double stroller in the trunk! We opted for a mini van (I know. Get the laughter out now) and it has been fantastic. The convenience of having automatic sliding doors, plenty of storage space, and seats where I don't have to lift the car seats above my head to get them latched in has far outweighed my embarrassment at driving a mini van.
Baby carrier-whether you prefer an ergo baby, mobe wrap, sling, or baby bjorn, gets baby carrier of some sort. There will be times when you will have two sad babies that just want to be held, and it's far easier to do it with one in a baby carrier and one in your arms than hold them both with only one arm each.
Double stroller-we went with a BOB so that I could easily take the kids both out jogging, and I love it. However, if I could do it again, I would also get a stroller that we could clip the car seats into.
Twin nursing pillow and double electric breast pump-if you plan on breast feeding. I have the MyBrest Friend twin size nursing pillow and I LOVE it. I don't think I would have stick with tandem feeding if I didn't have it. And a good double electric breast pump will help a lot with your supply. For the first month I pumped at least 3 times a day to get my supply up. And another positive, my mom, husband and friends were able to help feed the kids during those difficult early weeks using the milk I had pumped.
Podee bottles-seriously these things are amazing. Even if you plan to breast feed exclusively, I would suggest having a couple of these bottles on hand. Bottle feeding two babies at once is really tricky business. These bottles allow the baby to hold the nipple in their mouth themselves (like a pacifier) without having to grip and hold up the bottle. The milk come up from the bottle to their nipple in their mouth through a small tube as they suck. Amazing!
Feeding tracking system-especially in the early weeks when the babies are on different eating schedules, it is so helpful to have some way of recording and tracking when they eat. We used the BabyConnect app on our iPad. It allowed us to track eating, wet/dirty diapers, sleep patterns etc. for both babies.
Diaper bag with backpack type straps-my husband gave me a PPB diaper bag for Christmas and it has been amazing. Before that, I used a bag that just had a single shoulder strap but when you're alone and trying to carry a diaper bag in addition to two kids in car seats, having a bag that can fit on like a backpack is the best thing ever. Also, the straps on my bag have hooks that I use to hang grocery bags on when coming back from the store. I look like a pack mule but I love not having to take multiple trips!
Two high chairs and lots of bibs-when you are feeding two kids at the same time, it just gets messy. We go through bibs like they're going out of style. And having two high chairs is a must.
Changing pad?-we have one and we used it a lot when the babies were newborn, especially when my husband was home to help me. But when I'm alone, I find it's easier to lay a blanket down on the floor, put the babes on it and change their bums down there. So I would says changing pad ca be nice, but not a necessity.
Diaper Genie-to me, this is a necessity. We live in an apartment so it's not practical to run each smelly diaper outside immediately or even to set it out on the porch. The Genie does a great job of containing the smell while the diapers are stuck inside with us.
Storage-baby clothes take up a lot of space, especially when you have double the normal amount. We bought 4 plastic sliding drawer sets from Target that have 3 drawers each. So each baby has 6 drawers. In the top drawers I put the size they are currently wearing, then in the drawers underneath I have the next size ready to go. As they grow out of each size, I rotate them um through the drawers and put the too-small size in clear, labeled plastic totes in the top of the closet.
Lots and lots of diapers-we toyed with the idea of using cloth diapers to save money, but for two babies we decided the amount of laundry I'd need to do would be ridiculous. So we went with disposables. When they were newborn, we went through about 16 diapers/day. Now we are down to about 10/day. Which means that we spend $60-$80/month on diapers.
Well there you have it, my must-haves for surviving the first 6 months with twin babies!