I'm 14 weeks along with twins... for one we weren't planning on getting very much stuff b/c we still have a lot left over from DS. But I'm curious. Is there anything that is essential for twins that wouldn't be essential for a singleton? What should we get two of? And what can they share? What might not be technically "essential" but really helpful and worth it?
essential twin gear?
Two car seats. A twin nursing pillow was a must-have for me. We loved having a twin stroller (though for the early days we put them together in one stroller...even if you didn't use a stroller for your first). A Moby you can use for both babies, and eventually two slings (for front and back or side and side or you and a second adult). Other than that...we used more of things (more onesies, more diapers), but you may have enough as it is.
We did some color-coding of ours to help people tell them apart. Two different colors of safety pins were useful, and we told people about the color code for gifts. (not all gifts, but the ones from grandparents). Though mostly we just went through hand-me-downs and picked which to use.
I also really used and liked a twin nursing pillow. I'll agree with rinap, we used more of things, like diapers and clothes, but there were few things that we really needed two of. setting yourself up for help with the newborn stage or with your older child when you are almost due will be very helpful, as will a plan for who can bring meals/provide other help after the babies are born is another huge help.
The double stroller was not essential, but was and is pretty darn useful, I have one that I can snap their infant seat onto, it just makes getting out of the house 1000x easier. I agree that carriers are more essential with twins too as again it makes is easier to get out of the house too.
I too really like and use the twin nursing pillow and I didn't like any nursing pillows with DD1, just regular flat pillows.
I have found having two bouncy seats (or similar) and two bumbo seats (or similar) and two travel cribs (if you are going to travel) are all pretty essential. The bouncy seats are especially nice for showering and otherwise I keep one on each floor so I have a spot to stick one baby while I hold/nurse the other, they slept in them when they were really new. Bumbos for getting them more sitting up time since they don't get held as much. Travel cribs for sure as after a couple months they don't fit in one together and/or wake each other up too much.
I also found that having a changing station on every floor essential, with DD1, I just took her upstairs to change her diaper at the changing table every time, but it's easier with two infants to just stay on the same floor.
Two cribs are essential to me since I don't cosleep, but not at first. They can go in the same crib for a few months.
Otherwise, I am doing well with just more of everything: clothes, blankets, pacifiers, etc.
Definitely a changing station on every floor. We had a basket we could take to wherever the kids were, because that was easiest (one upstairs and one down).
We had a single crib sidecarred to the bed that the kids slept in until 6 months (together) and then we moved them to a floor bed. We also used one travel crib for them until about the same age (then we coslept when traveling)
My twin girls are almost 9 months old, and I have an older son who's 2.5. I found two rock n' plays to be very helpful for the first three months, especially once I was alone with all three kids and no one else could help hold the girls. The rock 'n plays were more like cradles than bouncy seats, so the girls could use them right from the beginning, and I liked that the rock 'n plays were higher off the ground--which meant the babies were more protected from Big Brother. (He seemed to just be more attracted to picking on them once they were in bouncy seats lower to the ground.) I also liked to use the rock 'n plays to help me transfer the girls when nursing them (when I didn't have someone else around to help). So while we only used them for a short time period, I did find them quite helpful. We started with just one (we had it from when my son was a baby), but friends bought us another, and it was very helpful to have two. (Just as a warning, though, my son really didn't like the rock 'n play when he was tiny--so part of the usefulness may depend on the temperament of the baby!)
I second the recommendation of a twin stroller. We actually own two--one with side-by-side seating, and one with front-back seating. The side-by-side one is easier to maneuver, but it doesn't fit through all doorways. The front-back one is nice for narrower doorways, aisles, etc.
We cloth-diapered our first (using prefolds and covers), and we definitely needed to buy more diapers and covers (especially covers) for the girls.
My mom got us a bunch of extra receiving blankets, and those were nice to have on hand for the first months. Extra burp cloths were also nice.
Now that the girls are eating solids, two high chair-type booster seats are great. We have a small house and a small dining area, so we opted to get booster seats that strap onto chairs rather than buying high chairs. These take up less room and are easy to remove when we need extra chairs for guests, take to the grandparents', etc.
We never bought exersaucer-type equipment and haven't really missed it. We did use a swing briefly, but one swing and one bouncy seat seemed to work just fine for us--we had two spots to put the girls but didn't need doubles of both.